L  I  B  RAFLY 

OF  THE 

UNIVERSITY 

OT    ILLINOIS 


NATURAL  IIigTCRY-STRyEr" : ' 

550.5 
FI 

v.AjCop.Q. 


REMOTE  STORAGi 


LIBRARY 

UNIVERSITY  OF  ILLINOIS 

URBANA 


Field  Museum  of  Natural  History 

Publication  232 

Geological  Series  Vol.  IV,  No.  4 


ON  THE  HEAD  OF  THE  MACROPETALICHTHYIDS 

with  certain  remarks  on  the  head  of 
the  other  arthrodires 


BY 


Erik  A: son  Stensio 
Royal  State  Museum,  Stockholm 


Oliver  Cummings  Farrington 
Curator,  Department  of  Geology 


Chicago,  U.  S.  A. 

October,  1925 


PREFACE 

The  Museum  specimen  (P  1154)  on  which  the  following  paper  by 
Dr.  Stensio  is  chiefly  based,  is  from  the  Onondaga  (Corniferous) 
Middle  Devonian  limestone  of  Leroy,  Genesee  County,  New  York. 
The  original  collector  is  not  known  to  the  Museum.  The  specimen 
together  with  another  (P  11 55),  from  the  same  locality,  was  obtained 
by  the  Museum  from  Ward's  Natural  Science  Establishment,  Roches- 
ter, New  York,  in  1894.  Its  remarkably  complete  preservation  has 
enabled  Dr.  Stensio  to  make  the  profound  anatomical  study  that  is 
presented  in  the  following  pages. 

The  matrix  of  this  specimen  when  freshly  broken  is  seen  to  be  a 
dark  brown,  partially  crystallized  limestone.  This  limestone  is  some- 
what argillaceous  and  bituminous,  and  slightly  magnesian.  Here  and 
there  it  exhibits  the  inclusions  of  chert  which  are  characteristic  of 
Corniferous  limestones.  On  weathered  surfaces  the  matrix  is  chalk- 
white  in  color,  Upon  which  the  dull  black  parts  of  the  fossil  fish  stand 
out  in  contrast. 

In  specimen  P  11 55,  only  the  dermal  bones  of  the  cranial  roof  of  a 
Macropetalichthys  are  preserved.  This  head  is  larger  than  that  of 
P  1 1 54,  being  19  centimeters  in  length  as  compared  with  12  centimeters 
in  P  1 1 54.  The  width  (12  centimeters)  is  about  the  same  for  both. 
The  plates  preserved  in  the  larger  specimen  are  of  a  dark,  calcareous 
substance,  about  1  mm.  thick.  Except  for  a  black  pigment,  this  sub- 
stance dissolves  readily  in  dilute  hydrochloric  acid.  On  removal  of  the 
remains  of  these  plates,  imprint  of  a  pustulose  external  surface  can  be 
plainly  seen  on  the  overlying  rock.  In  the  limestone  matrix  of  both 
specimens,  numerous  aggregates  of  more  or  less  comminuted  brach- 
iopod  shells  and  crinoid  stems  are  visible.  Among  the  brachiopods  so 
preserved,  individuals  of  the  species  Leptaena  rhomb  oidalis  and  A  try  pa 
reticularis  can  be  identified. 

Oliver  C.  Farrington. 


87 


ON  THE  HEAD  OF  THE  MACROPETALICHTHYIDS 

WITH     CERTAIN    REMARKS    ON    THE    HEAD    OF    THE    OTHER   ARTHRODIRES 

BY 

Erik  A:  son  StensiS 


CONTENTS 

Introduction 91 

Description  of  the  Macropetalichthyids 92 

Macropetalichthys  rapheidolabis 92 

Primordial  neurocranium : 

General  remarks 92 

Occipital  region 95 

Labyrinth  region 103 

Labyrinth  cavity 116 

Orbitotemporal  region 119 

Ethmoidal  region 129 

Cavum  cerebrale  cranii  and  brain 134 

Dermal  bones  of  the  primordial  neurocranium 140 

Dermal  bones  of  the  cheek 143 

Visceral  skeleton 144 

Dentition 146 

Sensory  canals  of  the  head 146 

Macropetalichthys  agassizi? 150 

Macropetalichthys  pelmensis 152 

Epipetalichthys  wildungensis,  gen.  nov.,  sp.  nov. 
Primordial  neurocranium: 

General  remarks 152 

Microscopic  structure  of  the  bone 153 

Occipital  region 154 

Labyrinth  and  orbitotemporal  region , 155 

Ethmoidal  region 156 

Cavum  cerebrale 157 

Dermal  bones  of  the  cranial  roof 157 

Sensory  canals  of  the  head 158 

Some  general  remarks  on  the  Macropetalichthyids 160 

Certain  remarks  concerning  the  other  non-Macropetalichthyid 

Arthrodires 164 

The  Phlyctenaspids 165 

The  Coccosteids 1 70 

The  Homosteids 180 

The  Mylostomids 180 

The  Ptyctodontids 181 

The  Jagorinids 182 

Some  general  remarks  on  the  non-Macropetalichthyid  Arthrodires.  186 

Concluding  remarks  on  the  affinities  of  the  Arthrodires 187 

Bibliography 191 

Explanation  of  Plates 198 

89 


INTRODUCTION 

As  the  holder  of  a  scholarship  from  the  University  of  Upsala  and 
with  support  from  the  Palaeontological  Museum  of  Kristiania,  I  under- 
took in  1922  a  journey  to  the  United  States  of  America  for  the  study 
of  certain  groups  of  fossil  vertebrates,  especially  Ostracoderms  and 
Arthrodires. 

In  examining  the  collection  of  the  Arthrodires  in  Field  Museum 
of  Natural  History  at  Chicago  I  found  a  specimen  of  Macropetcdichthys 
raphcidolabis,  (Field  Museum  Cat.  No.  P  1154),  that  if  prepared  in  a 
proper  way  was  likely  to  show  the  primordial  neurocranium  rather  com- 
pletely preserved.  Through  the  courteous  assistance  of  Mr.  H.  W. 
Nichols,  Associate  Curator  of  Geology  of  the  Museum,  permission  was 
secured  for  me  to  carry  out  the  preparation  of  the  specimen  which  I 
found  necessary  for  my  studies.  While  carrying  on  this  work  it  soon 
became  evident  that  the  specimen  was  of  much  greater  importance  from 
the  anatomical  point  of  view  than  I  at  first  thought;  for  most  of  the 
canals  for  nerves  and  vessels,  the  entire  cavum  cerebrale  and  a  part  of 
the  labyrinth  cavity  were  in  such  a  good  state  of  preservation  that  they 
could  be  examined  in  detail.  I  spent  ten  days  working  with  the  speci- 
men and  during  this  time  the  photographs  reproduced  in  Pis.  XIX- 
XXVI  were  made  by  the  photographer  of  the  Museum.  (Cf.  Annual 
Report  of  the  Director,  Field  Museum  of  Nat.  Hist.,  Publication  213. 
Report  series,  Vol.  VI,  No.  2,  p.  121.) 

The  present  paper  is  chiefly  based  on  the  specimen  of  Macropeta- 
UcJithys  rapheidolabis,  in  Field  Museum  of  Natural  History  at  Chicago, 
that  has  just  been  referred  to.  But  as  this  specimen  was  imperfect 
regarding  the  occipital  region,  this  was  studied  on  certain  specimens  in 
the  American  Museum  of  Natural  History  in  New  York,  a  few  of 
which — those  figured  in  this  paper — were  sent  to  me  in  1923  in  Sweden 
for  a  re-examination  in  certain  respects. 

The  specimen  of  the  new,  interesting  form  Epipetalichthys  wildun- 
gcnsis  described  in  the  present  paper  was,  in  the  most  courteous  way, 
placed  at  my  disposal  by  Professor  O.  Jaekel  of  Greifswald,  and  for 
the  opportunity  to  examine  the  specimen  described  below  under  the 
name  of  Macropetcdichthys  agassisi?  I  am  indebted  to  Mr.  S.  Junker- 
mann  of  Bielefeld. 

9i 


92      Field  Museum  of  Natural  History — Geology,  Vol.  IV. 

It  is  a  pleasant  duty  for  me  to  express  here  my  most  sincere  thanks 
to  Mr.  H.  W.  Nichols,  of  Field  Museum  of  Natural  History,  for  all 
the  help  I  received  from  him  and  for  the  kindness  he  showed  to  me 
during  my  stay  at  Chicago.  Further  I  wish  to  express  hearty  thanks 
to  Dr.  W.  K.  Gregory  and  Dr.  W.  D.  Matthew  for  their  help  in 
facilitating  my  studies  at  the  American  Museum  of  Natural  History 
in  New  York,  and  for  their  great  kindness  in  sending  material  to  me 
in  Sweden.  Finally,  I  am  also  highly  indebted  to  Professor  O.  Jaekel 
of  Greifswald,  both  for  the  material  which  I  received  from  him  for 
this  paper  and  for  important  information  concerning  the  Wildungen 
Arthrodires  upon  which  he  is  working. 

All  the  drawings  for  this  paper  were  made  by  Mr.  G.  Liljevall, 
of  Stockholm. 

DESCRIPTION  OF  THE  MACROPETALICHTHYIDS 

MACROPETALICHTHYS   RAPHEIDOLABIS 
Norwood  &  Owen 

(Pis.  XIX-XXVII,  PI.  XXVIII,  figs.  3-5J  PI.  XXX,  fig.  2;  PI.  XXXI,  fig.  1) 
PRIMORDIAL  NEUROCRANIUM 

General  Remarks.  The  primordial  neurocranium  is  strikingly 
broad  and  low,  its  maximum  width  almost  equalling  the  length  and  its 
maximum  height  constituting  only  about  one-seventh  of  the  length  and 
between  one-fifth  and  one-sixth  of  the  maximum  width  (Figs.  1,  3, 
5,  8;  Pis.  XIX-XXII;  PI.  XXIV,  figs.  1,  3).  The  maximum  height 
is  situated  in  the  posterior  and  the  maximum  width  in  the  anterior  half 
of  the  labyrinth  region. 

As  is  seen  from  text  figs.  4,  5,  8,  9,  and  PI.  XXIV,  figs.  1,  3,  the 
primordial  neurocranium  is  so  arched  both  in  a  transversal  and  longi- 
tudinal direction,  that  its  dorsal  surface  is  convex  and  its  ventral  sur- 
face correspondingly  concave. 

Concerning  the  shape  of  the  different  divisions  of  the  primordial 
neurocranium,  it  may  be  especially  pointed  out  in  this  connection  that 
the  occipital  and  ethmoidal  regions  have  a  considerable  length,  while 
the  labyrinth  and  orbitotemporal  regions  are  short.  The  latter  region 
is  even  strikingly  short  and  at  the  same  time  very  broad,  its  length 
being  only  about  one-half  of  the  width,  a  condition  which  is  due  partly 
to  the  slight  development  of  the  orbits  and  partly  to  the  considerable 
width  of  the  skull  as  a  whole.  With  regard  to  the  orbits,  it  is  in  addi- 
tion noteworthy  that  they  have  shifted  some  distance  backwards  and 
medially  and  that  they  are  much  directed  upwards. 


Macropetalichtiiyids  and  other  Arthrodires — Stensio      93 

The  primordial  neurocranium  consisted  of  cartilage  and  bone,  the 
latter  containing  fairly  numerous  cell  spaces.  The  bone  occurs,  how- 
ever, only  as  thin  layers,  which  covered  the  cartilage  on  the  cerebral 
surface,  within  the  labyrinth  cavity,  to  a  large  extent  on  the  external 
surface,  and  in  addition  also  formed  a  lining  membrane"  for  all  the 
canals  for  the  vessels  and  nerves  piercing  the  walls  of  the  neurocra- 
nium. Accordingly,  there  may  be  distinguished  an  internal  bone-layer, 
a  labyrinth  bone-layer,  an  external  bone-layer  and  canal  bone-layers. 
More  closely  defined,  these  different  layers  of  bone,  which  evidently 
are  perichondral,  have  the  following  extension  and  relations: 

i.  The  internal  layer  forms  a  continuous  covering  of  the  cerebra/ 
surface  of  the  primordial  neurocranium.  In  other  words,  it  lines  ihe 
whole  cavum  cerebrale  cranii. 

2.  The  labyrinth  layer  forms  a  continuous  lining  membrane  of  the 
whole  labyrinth  cavity  (cavities  for  the  semicircular  canals  included). 

3.  The  external  layer  covers  the  outside  of  the  primordial  neuro- 
cranium ventrally,  laterally  and  posteriorly,  but  dorsally,  on  the  con- 
trary, only  in  the  posterior  narrow  division  of  the  occipital  region  and 
probably  in  a  short  anterior  part  of  the  ethmoidal  region.  The  remain- 
ing parts  of  the  dorsal  side  of  the  occipital  and  ethmoidal  regions,  as 
well  as  the  whole  dorsal  side  of  the  labyrinth  and  orbitotemporal  re- 
gions, are  destitute  of  a  perichondral  bone-layer,  so  that  the  cartilage 
must  have  appeared  there  to  the  extent  shown  in  Fig.  3.  The  por- 
tion of  the  external  layer  covering  the  posterior  side  of  the  anterior 
broad  part  of  the  occipital  region,  is  connected  with  the  inner  layer  by 
a  few,  chiefly  sagitally  placed,  laminae  of  bone,  which  passed  through 
the  cartilage,  and  which  naturally  are  enchondral. 

4.  The  canal  layers  line  all  the  canals  traversing  the  cranial  walls, 
even  canals  and  branches  of  canals  with  a  very  narrow  diameter.  In 
those  cases  where  the  canals  pass  from  the  cavum  cerebrale  to  the  out- 
side, the  layers  lining  them  are  continuous  with  and  connect  the  external 
and  internal  bone  layers  with  one  another.  In  a  similar  way  the  internal 
layer  is  continuous  with  the  labyrinth  layer  by  layers  lining  such  canals 
which  run  from  the  cavum  cerebrale  to  the  labyrinth  cavity. 

The  different  layers  of  bone  just  described  actually  form  by  their 
connections  with  each  other  a  single  large  bone  extending  throughout 
the  length  of  the  primordial  neurocranium.  That  this  large  bone  was 
formed  by  the  coalescence  of  a  few  smaller  ones  seems  not  improbable, 
since  vestiges  of  ossification  centres  perhaps  occur  in  certain  places. 


94      Field  Museum  of  Natural  History — Geology,  Vol.  IV. 


elf- 

s.pal  -  -  - 

c.pal3 

N^S^ 

JU'-%* 

c. 

car.ext-M« 

chy- 


-f.arthnv 


^cr.Sp 


hcem. 


Fig.  i.     Macropetalichthys  rapheidolabis 

Restoration  of  primordial  neurocranium  in  ventral  aspect.  Occipital  region 
after  specimens  in  the  American  Museum  of  Nat.  Hist.,  New  York,  other  regions 
after  a  single  specimen  in  Field  Museum  of  Nat.  Hist.,  Chicago.  The  dimensions 
of  the  occipital  region  probably  not  fully  correct  in  relation  to  those  of  the  other 
regions.    Cartilage  dotted.     X^- 

c.car.ext,  canal  for  the  arteria  carotis  externa;  c.hy,  canal  for  the  vena 
hyoidea;  ch.w,  ridge  caused  by  the  most  anterior  part  of  the  notochord;  c.pah, 
opening  for  the  r.  palatinus  facialis ;  era,  canal  for  the  radix  aortae ;  cr.ol,  crista 
occipitalis  lateralis ;  cr.sp,  cranio-spinal  process ;  dix,  probable  foramen  for  the 
dorsal  branch  (lateralis  branch)  of  the  n.  glossopharyngeus ;  f.art.hm,  probable 
place  of  articulation  for  the  dorsal  end  of  the  hyoid  arch ;  ham,  haemal  groove ; 
ju,  canal  traversed  in  the  anterior  part  by  the  vena  mandibularis ;  in  the  longer 
posterior  part  by  the  v.jugularis  (behind  the  confluence  between  this  and  the 
vena  mandibularis)  ;  jiix  and  juz,  anterior  and  posterior  openings  of  the  canal  ju, 
the  anterior  one  traversed  by  the  vena  mandibularis ;  na,  nasal  opening ;  nf,  nasal 
fontanelle;  n.l,  canal  for  the  n.lineae  lateralis;  olf,  olfactory  capsule;  pr,  postero- 
lateral process  of  the  anterior  broad  division  of  the  occipital  region;  s.pal,  groove 
for  the  r.palatinus  facialis ;  s.ra,  groove  for  the  radix  aortae ;  Sx,  groove  leading 
some  distance  anteriorly  from  the  external  opening  of  the  vagus  canal;  IX,  canal 
for  the  n.  glossopharyngeus;  Xxn,  canal  for  the  n.vagus  and  the  vena  cerebralis 
posterior. 


Macropetalichthyids  and  other  Arthrodires — Stensio      95 

The  position  of  these  presumed  centres  is  seen  in  Figs.  I  and  3, 
and  will  be  further  dealt  with  in  the  subsequent  description  of  the  dif- 
ferent regions  of  the  primordial  neurocranium. 

Occipital  Region 

The  occipital  region  is  very  long,  its  length  probably  being  continued 
between  two  and  three  times  into  the  length  of  the  primordial  neuro- 
cranium (Figs.  1,  3,  5;  PI.  XXVII;  PI.  XXVIII,  figs.  4,  5).  With 
regard  to  its  shape  otherwise  it  may  be  considered  as  composed  of  two 
divisions,  an  anterior  one  and  a  posterior  one. 

The  posterior  one  of  these  divisions  (Figs.  1,  3,  5;  PI.  XXVII; 
PI.  XXVIII,  figs.  3-5;  PI.  XXX,  fig.  2)  is  much  longer  than  the 
anterior  one  but,  on  the  other  hand,  considerably  narrower  and  lower. 
With  the  longer  anterior  part  it  does  not  by  far  extend  up  to  the 
cranial  roof.  At  its  posterior  end  it  has  a  paired  laterally  and  dorsally 
projecting  process  (cr-sp),  which  is  coalesced  with  its  fellow  of  the 
other  side  medially  and  so  connected  on  the  anterior  side  with  a 
descending  lamina  from  the  posterior  bones  in  the  dermal  cranial  roof 
that  it  forms  a  support  for  these.  The  process  much  resembles  the 
cranio-spinal  process  in  Acipenscr,  Polyodon  and  Saurichthys  (Huxley 
1864,  Fig.  82;  Parker  1882,  PI.  15,  fig.  13;  PI.  16,  figs.  1,  3;  Iwanzow 
1887,  PI.  1,  fig.  2;  Gegenbaur  1912,  pp.  319-325;  Stensio  1925)  and 
may  therefore  be  termed  a  cranio-spinal  process  although  it  obviously 
has  evolved  independently  of  that  in  the  fishes  enumerated. 

The  most  postero-ventral  part  of  the  posterior  division  situated 
beneath  that  from  which  the  cranio-spinal  process  issues  is  not  found 
preserved  in  any  of  the  specimens  investigated,  a  fact  which  seems  to 
indicate  that  it  lacked  the  external  bone  layer  and  thus  was  entirely 
cartilaginous  when  seen  from  the  outside  (Figs.  1,  3,  5;  PI.  XXVII; 
PI.  XXVIII,  figs.  3-5;  PI.  XXX,  fig.  2).  It  probably  had  a  paired 
condyle  or  a  paired  fossa  for  articulation  with  the  vertebral  column, 
as  a  cranio- vertebral  joint  might  have  been  present  as  in  ordinary 
Arthrodires. 

Two  transverse  sections  through  the  posterior  division  are  shown 
in  text  fig.  2.  As  is  understood  from  these  and  Fig.  5,  the  pos- 
terior division  is  much  flattened  in  a  dorso-ventral  direction,  its  height 
being  only  about  one-half  of  the  width.  As  a  consequence  of  the  flat- 
tening, the  external  surface  has  no  lateral  fields,  but  only  a  dorsal  and 
a  ventral  field  separated  from  each  other  by  a  paired,  well  pronounced 
lateral  crista,  the  crista  occipitalis  lateralis  (cr.ol).  The  dorsal  one  of 
the  two  fields,  which,  as  mentioned  above,  is  situated  deep  below  the 


96      Field  Museum  of  Natural  History — Geology,  Vol.  IV. 

dermal  cranial  roof  except  at  the  posterior  end,  is  provided  with  a 
longitudinal  unpaired  crista,  the  crista  occipitales  dorsalis  (cr.od),  while 
the  ventral  field,  on  the  contrary,  has  a  wide  and  deep  longitudinal 
groove.  This  groove  (ham,  Figs,  i,  2;  PI.  XXVIII,  figs.  3,  4) 
constitutes  undoubtedly  an  anterior,  cephalic  portion  of  the  haemal 
groove  of  the  vertebral  column,  and  may  therefore  properly  be  termed 
the  haemal  groove.  Towards  the  transition  of  the  anterior  division  of 
the  region,  it  becomes  gradually  shallower  and  seems  to  divide  there 
into  two  shallow  branches  (Fig.  1;  PI.  XXVII,  fig.  4),  a  right  and 
a  left  one,  each  of  which  is  continued  forwards  by  the  groove  s.ra 
which  will  be  further  dealt  with  below  in  another  connection. 

The  part  of  the  cavum  cerebrale  cranii  situated  within  the  pos- 
terior division  is  long  and  low  and  narrow  in  comparison  with  those 
in  front  of  it.  It  is,  however,  somewhat  narrower  in  its  anterior,  than 
in  its  posterior  portions,  as  is  well  shown  by  Fig.  10  and  PI.  XXVII, 
fig.  1.    A  transverse  section  through  its  posterior  half  is  seen  in  Fig.  2. 

The  notochord  extended  into  the  basal  part  of  the  neuro-cranium, 
but  was  very  slightly  developed  there  (ch,  Fig.  2)  and  reached 
forwards  only  to  about  the  transition  between  the  anterior  and  posterior 
divisions  of  the  occipital  region  (PI.  XXVIII,  fig.  4).  It  was,  thus, 
in  the  neurocranium,  limited  to  the  posterior  division  of  the  occipital 
region,  while  the  parts  of  it  that  originally  existed  further  forward 
as  far  as  to  the  dorsum  sellae  have  become  reduced.  The  persistent 
part  was  surrounded  by  a  thin  bone  layer  of  its  own,  and  this  bone 
layer,  which  is  well  preserved  in  the  fossil,  forms  a  fine  longitudinal 
tube,  a  tube  which  is  coalesced  with  the  inner  bone  layer  dorsally  and 
the  external  bone  layer  (for  explanation  of  these  bone  layers  see  p. 
93  ventrally  at  the  bottom  of  the  haemal  groove  (Fig.  2).  In  the 
anterior  part  of  the  haemal  groove  the  notochord  has  pressed  the 
external  bone  layer  downwards  as  a  ridge,  the  notochordal  ridge  (ch.w), 
which  is  conspicuous  when  the  haemal  groove  is  seen  from  below  or  in 
transverse  section  (Figs.  1,  2B ;  PI.  XXVIII,  fig.  4). 

The  slight  development  of  the  cephalic  portion  of  the  notochord  of 
the  fish,  forms,  it  seems  to  me,  a  support  for  the  view  advanced  above, 
that  there  was  a  kind  of  articulation  between  the  head  and  the  body  as 
in  typical  Arthrodires.  (Adams  1919,  pp.  123-127;  Dean  1901,  Figs, 
pp.  116-117;  Eastman  1908a,  pp.  113-149;  1908b,  pp.  158-205;  Jaekel 
1902,  p.  106;  1907,  p.  171;  1919,  pp.  96-108;  etc.)  Such  an  articula- 
tion required  of  course  a  considerable  weakening  of  .the  notochord  at 
the  transition  between  the  vertebral  column  and  the  occipital  region  of 
the  neurocranium,  and  if  such  a  weakening  took  place  the  cephalic  por- 


Macropetalichthyids  and  other  Arthrodires — Stensi6      97 

tion  of  the  notochord  must  evidently  have  lost  its  importance  and 
decreased  in  width  and  extension,  just  as  it  has  done  in  recent  Chi- 
maeroids,  which,  as  we  know,  have  a  sort  of  cranio-vertebral  articula- 
tion. 

From  its  very  considerable  length  it  would  be  expected  that  the 
posterior  division  of  the  region  consisted  of  a  rather  large  number  of 
coalesced  segments,  and,  accordingly,  that  it  was  pierced  by  numerous 
canals  for  spino-occipital  nerves.  No  canals  of  this  kind  could,  how- 
ever, be  found  on  the  material  investigated,  and  it  is  therefore  impos- 
sible at  present  to  decide  anything  with  certainty  concerning  the  num- 
ber of  segments  composing  the  division. 

The  anterior  division  of  the  region,  if  we  now  proceed  to  this 
(Figs,  i,  3,  5;  Pis.  XIX-XXIV;  PI.  XXV,  figs,  i,  2;  PI.  XXVI,  figs.  I, 
2;  PI.  XXVII,  fig.  i),  is,  as  already  pointed  out,  much  shorter,  but,  on 
the  other  hand,  considerably  higher  and  broader  than  the  posterior  one. 
Anteriorly,  its  dimensions  are  equal  to  those  in  the  adjacent  part  of  the 
labyrinth  region,  so  that  it  is  really  in  no  way  marked  off  from  this. 


Mi  i  f  .  \_i  iti  iTif  >        rr  nr 

heem. 

Fig.  2.     Macropetalichthys  rapheidolabis 

A.  Transverse  section  through  the  anterior  part  of  the  posterior  half  of  the 
posterior  division  of  the  occipital  region. 

B.  Transverse  section  through  the  anterior  half  of  the  same  division  (accord- 
ingly taken  posterior  of  A). 

After  specimens  in  the  American  Museum,  New  York.  Bone  layers  with 
black,  continuous  lines.     Cartilage  dotted.     Xi- 

ch,  cavity  for  the  chorda  dorsalis;  ch.w,  ridge  in  the  haemal  groove  caused  by 
the  chorda  dorsalis;  cr.od,  dorsal  occipital  crista;  cr.ol,  lateral  occipital  crista; 
cv,  cavum  cerebrale  cranii;  ham,  haemal  groove. 

The  postero-latero-dorsal  corner  of  each  side  is  produced  backwards 
and  laterally  to  a  rather  large  process  supporting  the  lateral  parts  of 
the  dermal  cranial  roof. 

For  the  detailed  description  we  may  conveniently  consider  that  the 
anterior  division  of  the  region  is  composed  of  five  walls,  which  are  as 
follows :  a  ventral,  a  posterior,  a  right  and  a  left  lateral  and  a  dorsal. 
Of  these  the  ventral,  the  dorsal,  and  the  two  laterals  are,  as  is  evident 
from  the  figures,  directly  continuous  with,  and  in  no  way  marked  off 
from,  the  correspondingly  situated  ones  in  the  labyrinth  region. 

The  ventral  wall,  which  is  the  smallest  one  of  the  five,  is  as  a 
whole  narrow  in  comparison  with  the  dorsal,  although  it  rapidly  in- 


98      Field  Museum  of  Natural  History — Geology,  Vol.  IV. 

creases  in  width  forwards  (Fig.  i;  Pis.  XXI-XXIII).  As  is  well 
shown  in  PI.  XXIII;  PI.  XXV,  figs,  i,  2,  and  PI.  XXVI,  figs.  1,  2, 
ic  is  strikingly  thin,  especially  in  the  median  parts,  and,  as  already 
pointed  out,  the  notochord  was  entirely  reduced  in  it.  It  is  not  pierced 
by  any  canals  and  has  its  externa^  (ventral)  surface,  the  shape  of  which 
may  be  understood  from  text  fig.  1,  well  bounded  along  each  lateral 
border  by  a  sharp  edge.  ( 

The  posterior  wall  (Fig.  3;  PI.  XXIV,  fig.  3;  PI.  XXV,  fig.  2; 
PI.  XXVII,  fig.  1)  is  large  and  mostly  rather  thick.  Its  ventro-median 
parts  are  coherent  with  the  posterior  division  of  the  region,  its  dorso- 
median  parts  are  a  little  inclined  forwards  and  its  lateral  parts  stand 
approximately  vertical  or  may,  most  laterally,  be  inclined  a  little  back- 
wards. The  wall  is  covered  by  the  external  bone  layer  on  the  outside 
and  the  internal  bone  layer  on  the  inside,  as  are  also  the  other  walls, 
but,  as  mentioned  above,  it  is,  in  addition,  provided  with  a  few  sagittally 
running  bone  laminae  (Is,  PI.  XIX;  PI.  XXV,  fig.  2),  which  connected 
the  internal  and  external  bone  layers  with  one  another.  These  bone 
laminae  in  the  fresh  specimens  traversed  the  cartilage. 

The  external  surface  of  the  posterior  wall  has,  as  is  seen  from 
PI.  XXIV,  fig.  3,  a  considerable  extension,  which  faces  a  little  upward 
in  the  dorso-medial  parts  and  straight  backward  or  backward  and  a 
little  downwards  in  the  lateral  parts.  It  is  concave  both  in  the  trans- 
versal (Figs.  1,  3,  5;  Pis.  XIX-XXIV;  PI.  XXVII,  fig.  1)  and  dorso- 
ventral  directions  and  by  an  anterior  extension  of  the  crista  occi- 
pitalis dorsalis  (cr.od)  dorsally,  and  the  posterior,  narrow  division 
of  the  region,  vertically,  it  is  divided  into  a  right  and  a  left  half.  The 
internal  surface  of  the  same  wall,  that  is  lower  and  narrower  than 
the  external  one,  faces  forward  and  downward  (Fig.  11;  PI.  XX; 
PI.  XXIV,  fig.  3;  PI.  XXV,  figs.  1,  2;  PI.  XXVI,  figs.  1,  2)  and,  like 
the  external  one,  is  slightly  concave  both  in  transversal  and  dorso- 
ventral  directions. 

The  posterior  wall  is  perforated  by  a  paired,  rather  wide,  postero- 
laterally  running  canal  (n.l,  Figs.  1,  10,  11;  PI.  XXIV,  fig.  3;  PI. 
XXVII,  fig.  1),  which  has  its  external  opening  rather  far  laterally 
on  the  external  surface  of  the  wall.  This  canal  is,  as  will  be  evident 
from  facts  given  below,  a  branch  from  the  wide  vagus  canal  (Xvn) 
and  transmitted  the  n.  lineae  lateralis. 

The  dorsal  wall  (Fig.  3;  Pis.  XIX,  XX;  PI.  XXIV,  figs.  1,  3; 
Pi.  XXV,  figs.  1,  2;  PI.  XXVI,  figs.  1,  2)  has  a  very  considerable 
breadth  in  relation  to  its  length.  In  its  median  part  it  is  rather  thin, 
but  grows  rapidly  thicker  towards  the  lateral  parts.    It  is  much  arched 


Macropetalichthyids  and  other  Arthrodires — StensiG      99 

in  transversal  direction  so  that  the  convexity  faces  upwards.  As  has 
already  been  pointed  out,  it  has  no  external  bone  layer  (Fig.  3) 
and  no  definite  external  boundary.  Despite  this,  it  is,  however,  fully 
evident  that  its  upper  surface  had  no  fossae  or  depressions  for  por- 
tions of  the  trunk  muscles  penetrating  from  behind,  beneath  the  dermal 
bones,  for  the  external  bone  layer  of  the  posterior  wall  has  no  emar- 
ginations  in  its  upper  border  and  reaches  in  all  its  breadth  quite  up  to 
the  lower  surface  of  the  dermal  bones  above  it.  (PI.  XXIV,  fig.  3.) 
The  sensory  canals  of  the  cranial  roof  being,  as  we  shall  see,  situated 
in  rather  strongly  developed  ridges  on  the  lower  side  of  the  dermal 
bones,  the  upper  surface  of  the  dorsal  wall  of  the  primordial  neuro- 
cranium  must  have  had  grooves  for  these  ridges  in  the  way  shown 
in  text  figs.  3  and  5.  These  grooves  in  the  subsequent  description  will 
be  referred  to  as  sensory  canal  grooves.  (In  the  Field  Museum  speci- 
men (Pis.  XIX,  XX;  PI.  XXIV,  fig.  1)  the  dermal  bones  of  the  cranial 
roof  with  the  exception  of  those  parts  situated  deepest,  namely,  the 
sensory  canal  ridges,  have  weathered  away,  so  that  we  can  from  the 
conditions  there  easily  see  that  the  sensory  canal  ridges  must  have  been 
situated  in  grooves  on  the  upper  side  of  the  primordial  neurocranium) . 

The  canal  for  the  n.  lineae  lateralis  (n./.),  during  its  passage  through 
the  posterior  wall  of  the  division,  gives  off  several  fine  branches  in  a# 
more  or  less  straight  dorsal  direction.  These  fine  branches  (Id^-ldg, 
Pis.  XIX,  XX;  PI.  XXIV,  fig.  3;  PI.  XXVII),  which  number  at  least 
six  and  are  surrounded  in  their  total  length  by  a  thin  bone  layer,  pass 
upward  through  the  dorsal  wall  and  open  into  an  overlying  portion 
of  the  sensory  canal  system,  thus  having  a  course  that  fully  proves 
them  to  have  transmitted  lateralis  fibres  and  that  the  canal  from  which 
they  are  given  off  was  traversed  by  a  thick  lateralis  nerve.  As  the 
latter  canal  is  the  only  one  that  issues  backward  from  the  vagus  canal, 
and,  in  addition,  as  we  shall  see,  forms  the  sole  possible  way  backward 
to  the  abdominal  region  for  all  the  lateralis  fibres  that  accompanied 
the  vagus  roots  proper  at  the  exit  from  the  cavum  cerebrale  cranii,  it 
undoubtedly  transmitted  the  whole  n.  lineae  lateralis.  The  portion  of 
the  sensory  canal  system  of  the  head  innervated  from  it  is  thus  the 
cephalic  division  of  the  main  lateral  line  (Cf.  the  description  of  the. 
sensory  canal  system  below).  In  the  Field  Museum  specimen,  in  which 
the  dermal  bones  of  the  cranial  roof  have  weathered  away  and  certain 
parts  of  the  underlying  dorsal  and  posterior  walls  of  the  primordial 
neurocranium  have  split  off,  the  canal  for  the  n.  lineae  lateralis  and  its 
dorsal  branches  are,  as  may  be  seen  in  the  figures  mentioned,  beauti- 
fully displayed. 


ioo    Field  Museum  of  Natural  History — Geology,  Vol.  IV. 

Some  distance  medially  of  these  dorsal  branches,  a  rather  fine, 
paired  canal  (cl,  Figs.  3,  5 ;  Pis.  XIX,  XX)  goes  upward  through 
the  dorsal  wall  and,  after  arriving  close  to  the  upper  surface  of  this, 
turns  abruptly  medially,  continuing  in  this  direction  almost  until  it 
meets  its  fellow  of  the  opposite  side  in  the  median  line.  During  this 
superficial,  medially  directed,  ^art  of  its  course  it  sends  out  several 
branches  both  forward  and  backward.  It  could  not  be  traced  quite  to 
its  ventral  end  and  hence  a  positive  explanation  of  its  function  can 
not  be  given.  It  seems  most  probable,  however,  that  it  transmitted 
bundles  of  communis  and  general  cutaneous  fibres  from  the  vagus  to 
the  cranial  roof,  and  thus  transmitted  a  ramus  supratemporalis  vagi. 
Besides  this  it  may  perhaps  also  have  been  traversd  by  vessels  and,  in 
addition,  perhaps  by  a  branch  of  lateralis  fibres,  as  it  communicated  with 
the  canal  for  the  n.  linese  lateralis  by  a  fine  branch.  The  destination 
and  morphological  importance  of  this  possible  bundle  of  lateralis  fibres 
will  be  discussed  below  in  connection  with  the  description  of  the  sen- 
sory canal  system. 

The  lateral  walls  of  the  division  (Figs.  1,  5;  Pis.  XXI-XXIII; 
PI.  XXIV,  figs.  1,  2;  PI.  XXV,  figs.  1,  2;  PI.  XXVI,  figs.  1-4;  PI. 
XXVII,  fig.  1)  are  thick  throughout  their  extension,  the  thickness 
being,  however,  not  equal  in  all  parts  but  gradually  increasing  upwards. 
They  are  covered  by  the  external  bone  layer  on  the  outside  and  the 
internal  bone  layer  on  the  inside.  Each  has  its  external  surface  directed 
laterally  and  much  downwards  and  its  internal  surface  almost  straight 
medially.  A  distinct  but  rather  narrow  groove  (s.ra)  runs  along  the 
ventral  edge  of  the  external  surface,  a  groove,  which,  as  we  shall  see, 
continues  forward  on  to  the  external  surface  of  the  lateral  wall  of  the 
labyrinth  region  and  backwards  to  the  haemal  groove,  at  the  anterior 
end  of  which  it  meets  its  fellow  of  the  opposite  side  in  the  median 
line.  This  groove  undoubtedly  lodged  the  radix  aortse  (lateral  dorsal 
aorta)  of  its  side,  as  will  be  evident  from  the  account  of  the  labyrinth 
region  given  below. 

At  the  transition  to  the  labyrinth  region,  each  lateral  wall  is  pierced 
by  the  vagus  canal.  This  canal  (Xvn,  Figs.  5,  10,  11,  12,  13;  Pis. 
XX,  XXI;  PI.  XXIV,  fig.  2;  PI.  XXV,  figs.  1,  2;  PI.  XXVI,  figs. 
1-4;  PI.  XXVII,  fig.  1),  which  is  wide  and  on  account  of  the  thickness 
of  the  lateral  wall  at  this  place  has  a  fairly  considerable  length,  runs 
almost  straight  laterally  to  the  external  surface  of  the  lateral  wall, 
where  it  opens  with  a  wide,  rather  forward  facing  foramen  (XVD, 
Figs.  1,  5;  Pis.  XXII,  XXIII;  PI.  XXIV,  figs.  1,  2).  A  proximal 
short  part  of  it  is  much  higher  than  broad  (PI.  XXV,  figs.  1,  2;  PI. 


Macropetalichthyids  and  other  Arthrodires — Stensio     ioi 


XXVI,  figs.  I,  2)  and  exhibits  no  certain  evidence  of  subdivision  by 
longitudinal  septa. 

On  the  other  hand  the  remaining  distal,  and  by  far  longer,  part,  has 
a  more  circular  section  than  the  former  and  is  subdivided  into  two 
incompletely  separated  divisions,  a  narrow  and  a  wide  one,  by  two 
longitudinal  ridges,  divisions  which  perhaps  in  the  living  animal  were 
totally  separated  from  each  other  by  a  membrane  of  connective  tissue  ex- 
tending between  the  ridges.    In  the  proximal  part  of  the  distal  half  of 


-cr.sp 


Fig.  3.    Macropetalichthys  rapheidolabis 

Primordial  neurocranium  in  dorsal  view.  Occipital  region  after  specimens  in 
the  American  Museum,  New  York,  and  a  specimen  in  Field  Museum,  Chicago; 
other  regions  after  the  latter  specimen.  Perichondral  bone  with  a  dark  tone. 
Cartilage  dotted.     XV2. 

cl,  canal  probably  for  a  dorsal  branch  of  the  vagus  and  a  bundle  of  lateralis 
fibres;  cr.od,  dorsal  occipital  crista;  cr.ol,  lateral  occipital  crista;  cr.sp,  cranio- 
spinal process ;  d.end,  canal  for  the  ductus  endolymphaticus ;  f.end,  fossa  endo- 
lymphatica;  olf,  olfactory  capsule;  orb,  orbit;  par,  pineal  opening;  pfg,  cavum 
precerebrale ;  pr,  postero-lateral  process  of  the  anterior  broad  division  of  the 
occipital  region. 


io2    Field  Museum  of  Natural  History — Geology,  Vol.  IV. 

the  canal  the  narrow  division  (Xv,  Fig.  u;  PI.  XXIV,  fig.  2)  is 
situated  dorsally  of  the  wide  one  (Xn,  PI.  XXIV,  fig.  2),  but  during 
the  passage  outwards  they  gradually  change  their  mutual  position  so 
that  the  former  finally  lies  behind  the  latter  and  occupies  the  posterior 
portion  of  the  common  external  opening,  which  is  distinctly  broader 
than  high.     (PI.  XXIV,  fig.  rf{ 

From  conditions  in  other  fishes  we  may  conclude  with  great  prob- 
ability that  in  M.  rapheidolabis  the  narrow  one  of  the  two  divisions  just 
described  in  the  vagus  canal  transmitted  the  vena  cerebralis  posterior 
(v.  encephalica  posterior)  and  the  wide  one  the  vagus  proper  and  in 
the  proximal  half  the  n.  linear  lateralis  too.  For  the  vena  cerebralis 
posterior  in  all  fishes  which  have  been  closely  investigated  with  regard 
to  this,  arises  by  the  confluence  of  anterior  and  posterior  branches  from 
the  dorsal  side  of  the  medulla  oblongata  and  enters  the  cranial  wall 
dorsally  of  the  vagus  roots.  It  then  within  the  cranial  wall  usually 
turns  a  little  forward  and  crosses  the  vagus  roots  on  the  dorsal  side 
so  that  when  reaching  the  outer  surface  it  is  situated  just  in  front  of 
these  roots  and  not  as  in  M.  rapheidolabis  posterior  to  them.  In  cer- 
tain forms  it  runs  through  the  same  canal  with  the  vagus  roots,  in 
other  forms  it  is  more  or  less  completely  separated  from  them  by  a 
septum  of  bone,  cartilage  or  connective  tissue.  (Cf.  Stensio  1922,  p. 
172;  1925,  p.  21;  Grosser  1907,  Fig.  4;  O'Donoghue  1914,  p.  442; 
Pollard  1892a,  PI.  XXIX,  fig.  23;  Allen  1905,  pp.  87-89;  Rex  1891, 
Pis.  15,  16;  etc.)  Similar  conditions  were  also  found  in  a  specimen  of 
Chimcera  monstrosa,  which  was  dissected  by  me. 

During  the  passage  through  the  lateral  wall,  the  vagus  canal  in 
M.  rapheidolabis  gives  off  from  its  proximal  half  two  branches,  one  on 
the  posterior  and  the  other  on  the  anterior  side.  The  former  of  these 
O.Z,  Figs.  10,  11;  Pis.  XXI,  XXIII;  PI.  XXIV,  fig.  3;  PI.  XXVII, 
fig.  1),  which  issues  rather  low,  is  the  canal  for  the  n.  lineae  lateralis 
and  has  already  been  dealt  with  above  in  connection  with  the  descrip- 
tion of  the  posterior  and  dorsal  walls.  As  pointed  out  there,  it  runs 
postero-laterally  to  the  outer  surface  of  the  posterior  wall,  sending  out 
several  fine  branches  upwards  to  the  cephalic  division  of  the  lateral  line. 
The  other  branch  (dx,  Figs.  10,  11;  PI.  XXIV,  fig.  2),  which  is 
much  narrower  and  issues  much  higher  up  and  more  proximally,  runs 
some  distance  almost  straight  dorsally,  then  not  so  very  deep  below  the 
dorsal  surface  of  the  dorsal  wall,  bifurcating  into  an  antero-lateral  (dx&, 
PI.  XXIV,  fig.  2)  and  an  antero-medial  (dxh,  PI.  XXIV,  fig.  2) 
ramus,  each  of  which  has  a  superficial  course  beneath  a  sensory  canal 
division,  to  which  fine  ramuli  are  sent  out  in  a  dorsal  direction  (PI. 


Macropetalichthyids  and  other  Arthrodires — Stensio     103 

XXIV,  fig.  2).  And,  as  it  is  fully  evident  that  these  ramuli  must  have 
transmitted  nerves  to  the  sensory  canal  organs,  the  anterior  branch 
(dx)  from  the  vagus  canal  is  consequently  proved  to  have  transmitted 
a  dorsal  branch  from  the  n.  lineae  lateralis.  The  relations  of  this 
dorsal  lateralis  branch  will  be  treated  also  in  the  description  of  the 
sensory  canal  system  below. 

Into  the  proximal  half  of  the  vagus  canal  and,  more  exactly,  into 
the  dorsal  part  of  this  just  as  it  leaves  the  cavum  cerebrale,  there  opens 
a  wide  canal  {v. lb,  Figs.  10,  11 ;  PI.  XX,  XXIV,  fig.  2;  PI.  XXV, 
figs.  1,  2;  PI.  XXVI,  figs.  1,  2,  3),  which  comes  from  the  postero- 
dorso-medial  corner  of  the  labyrinth  cavity.  The  function  of  this  canal 
is  not  fully  clear,  but  it  seems  very  probable  that  it  transmitted  a  vein 
from  the  labyrinth  to  the  vena  cerebralis  posterior,  because  in  the 
Lorcati — the  only  teleostomous  fishes  investigated  in  detail  with  regard 
to  the  veins  of  the  head — there  is  a  small  vein  which  goes  from  the 
labyrinth  in  a  similar  way  back  to  the  v.  cerebralis  posterior  (Allen 
1905,  PI.  Ill,  figs.  23a,  23,  25).  This  vein  in  the  Loricati  receives 
blood,  as  it  seems,  merely  from  the  ampulla  posterior,  while  the  pre- 
sumed vein  in  question  in  M.  rapheidolabis ,  to  judge  from  the  large 
width  of  the  canal  v.lb,  must  have  received  blood  from  the  larger  part 
or  the  whole  of  the  membranous  labyrinth. 

At  the  transition  between  the  anterior  and  posterior  divisions  of 
the  region,  the  external  bone  layer  on  both  the  ventral  and  dorsal  side 
seems  to  show  a  certain  very  faint  radiation  from  a  median  unpaired 
centre.  Hence,  if  this  observation  is  true,  there  would  be  two  unpaired, 
vestigial  centres  of  ossification  in  the  region,  the  dorsal  one  of  which 
would  correspond  most  closely  to  the  centre  of  a  supraoccipital  bone, 
the  ventral  one  to  the  centre  of  a  basioccipital  bone.  Better  preserved 
material  than  that  investigated  by  the  author  is,  however,  needed  for 
a  positive  decision  in  this  case. 

The  part  of  the  cavum  cerebrale  cranii  enclosed  in  the  anterior 
division  of  the  region  increases  rapidly  both  in  height  and  breadth 
forwards.  Its  shape  is  well  shown  by  Figs.  10,  11,  12,  13,  PI.  XX, 
PI.  XXIII,  PI.  XXIV,  fig.  3;  PI.  XXV,  figs.  1,  2  and  PI.  XXVI, 
figs.  1,  2. 

Labyrinth   Region 

The  labyrinth  region  is  very  short  and  broad,  its  length  being  con- 
tained about  two  and  a  half  times  in  the  maximum  breadth.  It  is  also 
rather  low,  as  its  maximum  height  amounts  only  to  between  a  fourth  or 
a  fifth  of  the  maximum  breadth.  The  maximum  height  is  situated  far 
back,  almost  at  the  transition  to  the  occipital  region,  the  maximum 


104    Field  Museum  of  Natural  History — Geology,  Vol.  IV. 

breadth,  on  the  other  hand,  in  the  anterior  half  of  the  region  (Figs.  I, 
3,  4,  5;  Pis.  XIX-XXI,  XXIII;  PI.  XXIV,  figs,  i,  3;  PI.  XXV,  figs. 
1,  2;  PI.  XXVI,  figs.  1,  2).  As  shown  by  the  figures,  the  region  is 
arched  both  transversally  and  longitudinally,  so  that  the  dorsal  side  is 
convex  and  the  ventral  side  concave,  the  arching  being,  however, 
stronger  in  the  former  than  in  the  latter  direction.  The  antero-lateral 
corner  of  each  side  projects  forwards  as  a  large  postorbital  process, 
forming  not  only  a  posterior  but  also  to  a  large  extent  a  lateral  boundary 
of  the  orbit,  a  disposal  which  is  due  to  a  postero-medial  displacement  of 
the  orbit.  The  postorbital  process  is  ventrally,  throughout  its  length, 
continuous  with  the  extensive  orbital  floor  (Figs.  3,  8). 

For  the  detailed  description  we  may  consider  the  region  to  be 
composed  of  four  walls:  a  ventral,  a  dorsal  and  a  paired  lateral. 

The  ventral  wall,  if  we  first  turn  to  it  (Figs.  1,  4,  5;  Pis.  XXI, 
XXIII;  PL  XXV,  figs.  1,  2;  PI.  XXVI,  figs.  1,  2,  3),  is  comparatively 
thin  throughout  almost  its  entire  extension,  but  is  thinnest  in  the 
median  parts.  At  the  transition  to  the  occipital  region  it  is  fairly 
narrow,  but  grows  rapidly  broader  forwards,  finally  attaining  a  very 
considerable  width.  It  is  covered  both  by  the  internal  and  external 
bone  layers  and  perforated  by  certain  canals  in  the  lateral  parts  at 
the  transition  to  each  lateral  wall.  These  canals  will,  however,  not  be 
described  here,  but  in  connection  with  the  lateral  walls,  which  are  also 
perforated  by  them. 


Fig.  4.    Macropetalichthys  rapheidolabis 

Transverse  section  through  the  posterior  part  of  the  labyrinth  region.  Dermal 
bones  marked  with  vertical  lines.  Layers  of  substitution  bone  with  continuous  black 
lines.     Cartilage  dotted.    XM- 

Mi,  L3,  P2,  S,  bones  of  the  dermal  cranial  roof  (approximate  extensions). 
For  their  position  cf.  text  fig.  15.  c.pp,  sensory  canal  commissure,  probably  cor- 
responding to  the  posterior  head  line  of  pit  organs  in  fishes  in  general;  cv, 
cavum  cerebrale  cranii;  d.end,  canal  for  the  ductus  endolymphaticus  (ventral 
part)  ;  d™,  the  antero-lateral  branch  of  the  canal  d\  which  transmitted  a  lateralis 
branch  to  the  above-lying  sensory  canal ;  lab.cav,  labyrinth  cavity ;  Ic,  cephalic 
division  of  the  lateral  line;  s.ra,  groove  for  the  radix  aortae  (lateral  dorsal 
aortse)  ;  St,  groove  leading  some  distance  forward  from  the  external  opening  of 
the  vagus  canal. 


Macropetalichthyids  and  other  Arthrodires — Stensio     105 

The  dorsal  wall  of  the  region  (Figs.  3,  4,  5;  Pis.  XIX,  XX, 
XXIV;  PI.  XXV,  figs.  1,  2;  PI.  XXVI,  figs.  1-3)  is  broad  throughout 
its  extension,  its  breadth  being,  however,  larger  in  the  anterior  than  in 
the  posterior  half.  With  the  exception  of  its  lateral  parts,  situated 
above  the  labyrinth  cavities,  the  wall  must  have  been  rather  thick,  and, 
as  pointed  out  already  in  the  general  description  of  the  neurocranium, 
it  was  covered  only  by  the  internal  bone  layer,  so  that  the  dermal  bones 
of  the  cranial  roof  rested  on  its  cartilage.  The  external  (dorsal)  sur- 
face must  have  had  rather  pronounced  grooves  for  the  sensory  canal 
ridges  on  the  lower  sides  of  the  dermal  bones  of  the  cranial  roof,  as 
indicated  in  text  figs.  3,  4  and  5.  Far  back  on  the  dorsal  surface  there 
may,  in  addition,  have  been  a  paired  pit  (f.end)  at  the  bottom  of  which 
the  canal  for  the  ductus  endolymphaticus  (d.end,  Fig.  3;  PI.  XX; 
PI.  XXVI,  fig.  3)  opened,  for  this  canal  does  not  seem  to  extend  fully 
up  to  the  ventral  side  of  the  overlying  dermal  bones  (Pis.  XIX,  XX). 
In  other  words,  there  seems  to  have  been  a  fossa  endolymphatica. 

Besides  by  the  canal  for  the  ductus  endolymphaticus  mentioned, 
which  will  be  described  more  in  detail  below  in  the  account  of  the 
labyrinth  cavity,  the  dorsal  wall  must  have  been  pierced  by  several 
fine  canals  for  vessels  and  nerve  branches.  Two  of  these,  both  for 
lateralis  branches  to  a  portion  of  a  sensory  canal,  are  well  seen  in  the 
Field  Museum  specimen   (in,  Pis.  XX,  XXII). 

The  lateral  wall  of  each  side  is  very  thick,  especially  in  its  dorsal 
and  anterior  parts,  and  is  covered  by  both  the  internal  and  external 
bone  layers  (Figs.  1,  3,  4,  5;  Pis.  XX,  XXI,  XXIII,  XXIV). 
In  its  interior  it  contains  the  large  labyrinth  cavity  (lab.cav,  Fig.  4; 
PI.  XX;  PI.  XXVI,  figs.  3,  4;  PI.  XXVII),  which  is  completely  sep- 
arated from  the  cavum  cerebrale  cranii  by  a  rather  thick  septum  of 
cartilage,  covered  by  the  internal  bone  layer  on  the  cerebral  surface 
and  the  labyrinth  bone  layer  on  the  labyrinth  surface.  The  internal 
surface  of  the  wall  is  directed  almost  straight  medially.  The  external 
one  consists  of  two  fields,  an  anterior  and  a  posterior  one,  the  latter 
of  which  faces  ventrally  to  a  marked  degree,  while  the  former,  which 
forms  the  posterior  surface  of  the  orbital  cavity,  faces  mainly  for- 
wards. The  two  fields  are  separated  from  each  other  by  a  rounded 
edge  running  from  the  antero-dorsal  corner  of  the  postorbital  process 
a  short  distance  in  a  ventral  direction.  By  another,  although  indistinct 
dorso-ventral  edge  the  posterior  field  is  in  its  turn  subdivided  into  an 
anterior  and  a  posterior  part,  the  former  of  which  is  convex  both  in 
dorso-ventral  and  antero-caudal  directions  and  faces  almost  straight 
downwards,  while  the  latter,  on  the  contrary,  is  concave  in  the  same 


106    Field  Museum  of  Natural  History — Geology,  Vol.  IV. 

directions  and  faces  much  less  downwards,  but  in  addition  a  little 
backwards  (Figs,  i,  4,  5;  Pis.  XXI,  XXIII,  XXIV).  On  the 
latter  part  we  find  along  the  ventral  border  the  anterior  continuation 
of  the  groove  s.ra  (Figs.  1,  4,  5;  Pis.  XXI-XXIV)  already  re- 
ferred to  above  in  the  description  of  the  lateral  wall  of  the  anterior 
division  of  the  occipital  region,  and  at  the  transition  to  the  anterior 
part  of  the  same  field  this  groove  deepens  and  is  suddenly  transformed 
into  a  closed  canal  (era),  which  goes  forward  in  the  wall.  We  shall 
below  return  to  this  canal  (era)  and  the  groove  (s.ra)  leading  to  it 
and  try  to  make  out  what  their  functions  were.  Before  doing  this  we 
must,  however,  examine  the  canals  for  cranial  nerves  that  perforate 
the  lateral  wall,  beginning  with  the  glossopharyngeus  canal  and  pro- 
ceeding forwards. 

The  glossopharyngeus  canal  (IX,  Figs.  1,  5,  7,  10,  11;  Pis.  XXI- 
XXIII;  PI.  XXIV,  figs.  1,  2;  PI.  XXV,  figs.  1,  2;  PI.  XXVI,  figs. 
1,  2,  4;  PI.  XXVII),  which  is  fairly  narrow,  has  its  internal  opening 
situated  rather  far  anterior  of  the  vagus  canal  and  much  nearer  to 
the  floor  than  to  the  roof  of  the  cavum  cerebrale  cranii.  It  seems  to 
go  almost  straight  laterally  to  the  posterior  lower  part  of  the  labyrinth 
cavity,  continuing  from  this  cavity  with  about  the  same  direction  as 
before  to  the  external  surface  of  the  lateral  wall,  where  it  opens  in  the 
anterior  part  of  the  groove  s.ra,  and  accordingly  close  to  the  ventral 
edge  of  the  surface.  The  external  opening  is  incompletely  subdivided 
into  two  divisions  (Figs.  1,  5;  PI.  XXIV,  fig.  1),  an  anterior  and 
a  posterior  one,  the  latter  of  which  is  slightly  smaller  than  the  former. 

Somewhat  dorsally  of  the  external  opening  of  the  glossopharyngeus 
canal  there  are  traces  of  another,  although  finer,  canal  (dix,  Fig.  1 ; 
Pis.  XXI,  XXIII;  PI.  XXIV,  figs.  1,  2;  PI.  XXVII),  which  seems  to 
run  upwards  to  a  portion  of  a  sensory  canal,  piercing  during  its  passage 
the  dorsal  part  of  the  lateral  wall  and  the  overlying  lateral  part  of 
the  dorsal  wall.  Accordingly,  this  canal  has  a  course  which  seems  to 
indicate  that  it  may  have  contained  a  lateralis  nerve.  And  as  it  is  situ- 
ated almost  straight  above  the  external  opening  of  the  glossopharyngeus 
canal,  we  may  conclude  with  a  rather  high  degree  of  probability  that 
this  lateralis  nerve  arose  from  fibres  which  had  their  passage  through 
the  lateral  wall,  together  with  the  n.  glossopharyngeus,  as  is  the  case  in 
several  other  recent  and  fossil  fishes,  e.g.  Selachii.  (Ewart  and  Cole 
1895,  pp.  475-476;  Norris  and  Hughe  1920,  p.  358,  Figs.  51,  52,  53), 
Polypterus  (Pollard  1892a,  p.  397,  PI.  28,  fig.  13;  Lehn  1918,  pp. 
395-396;  Allis  1922a,  pp.  283-284),  Lepidosteus  (Veit  1907,  p.  187; 
191 1,  PI.  D,  figs.  2,  6,  10),  Amia  (Allis  1897,  p.  684),  Acipenser, 


Macropetalichthyids  and  other  Arthrodires — StensiG     107 

Polyodon  (Allis  1920,  pp.  138,  142;  observations  made  by  the  author: 
cf.  also  Stensio  1924),  Saurichthys  (Stensio  1925)  and  certain 
Teleostei  (Herrick  1901,  pp.  207-208,  PI.  XIV).  In  other  fishes  in 
which  the  conditions  are  known,  the  corresponding  lateralis  fibres  pass 
through  the  vagus  canal  associated  with  the  n.  lineae  lateralis. 

The  possible  lateralis  branch  which  has  just  been  dealt  with  may 
perhaps  be  thought  to  have  caused  the  bipartition  of  the  external  open- 
ing of  the  glossopharyngeus  canal.  And,  if  so,  it  seems  probable  that  the 
n.  glossopharyngeus  proper  passed  through  the  larger  anterior  and  the 
lateralis  nerve  through  the  smaller  posterior  division  of  the  opening. 

The  canals  for  the  n.  acusticus  (VIII)  and  the  n.  facialis  (VII) 
begin  proximally  in  a  common,  distinct  recess  (afr,  Figs.  10,  IX  J 
PI.  XXIII;  PI.  XXV,  figs.  1,  2;  PI.  XXVI,  fig.  2)  on  the  ventral 
part  of  the  lateral  side  of  the  cavum  cerebrale.  This  recess,  which  may 
be  properly  termed  the  acustico-facialis  recess,  communicates  in  the 
fossil  freely  with  the  cavUm  cerebrale,  but  was  perhaps  in  the  fresh 
specimens  separated  from  this  by  a  membrane  belonging  to  the  dura 
mater.  For  comparison,  it  may  here  be  mentioned  that  a  recess  of  a 
similar  kind  occurs  in  several  recent  fishes,  but  that  in  these  it  often 
has  a  larger  extension  forward  so  that  not  only  the  acusticus  and 
facialis  canals  but  also  the  trigeminus  canal  take  their  origins  from  it. 
On  account  of  this  fact  it  is  called  in  such  forms  the  acustico-trigemino- 
facialis  recess,  and  it  may  further  be  noted  that  it  sometimes  is  sep- 
arated there  from  the  cavum  cerebrale  by  a  thin  lamina  of  connective 
tissue  or  bone,  a  lamina  formed  by  the  dura  mater.  (Cf.  Allis  1909a, 
pp.  44,  4<>47>  i24;  i9!4a,  pp.  232-236,  239,  240,  243,  246-248;  1914b; 
1919a;  1922a,  p.  228.) 

The  acusticus  canal  (VIII)  of  M.  rapheidolabis,  which  is  rather 
wide,  goes  from  the  posterior  part  of  the  acustico-facialis  recess  almost 
straight  laterally  to  the  labyrinth  cavity,  piercing  the  ventral  part  of 
the  septum  that  separates  the  labyrinth  cavity  and  the  cavum  cerebrale 
from  one  another.  Its  position  in  relation  to  the  labyrinth  cavity  is 
shown  by  PI.  XXVI,  fig.  3,  in  which  the  septum  separating  that  cavity 
from  the  cavum  cerebrale,  however,  has  been  almost  entirely  removed. 

The  facialis  canal  (VII),  which  is  of  about  the  same  width  as  the 
acusticus  canal,  issues  from  the  anterior  part  of  the  acustico  facialis 
recess  (Figs.  10,  11 ;  PI.  XXV,  figs.  1,  2;  PI.  XXVI,  figs.  1,  2).  On 
account  of  the  thickness  of  the  lateral  wall  at  this  place  it  gets  a  con- 
siderable length.  It  runs  first  for  some  distance  forward  and  slightly 
laterally  close  to  the  antero-ventral  part  of  the  labyrinth  cavity 
(Figs.  10,  11 ;  PI.  XXV,  fig.  1 ;  PI.  XXVI,  fig.  3),  then  at  the  antero- 


108    Field  Museum  of  Natural  History — Geology,  Vol.  IV. 

ventro-medial  corner  of  this  cavity  it  suddenly  takes  a  more  lateral  and 
ventral  direction  (Figs.  10,  n;  PI.  XXV,  figs,  i,  3;  PI.  XXVI, 
figs.  3,  4)  and  continues  with  this  course  to  the  external  opening  (text 
fig.  1;  Pis.  XXI-XXII;  PI.  XXIV,  fig.  1),  close  posterior  to  the 
antero-ventral  corner  of  the  posterior  field  of  the  external  (lateral) 
surface  of  the  lateral  wall.  The^more  laterally  and  ventrally  running 
part  is  situated  immediately  anterior  of  the  labyrinth  cavity  between 
this  and  the  orbit.  As  may  be  understood  from  PI.  XXVI,  fig.  3, 
the  part  of  the  lateral  wall  separating  the  orbit  and  labyrinth  cavity 
from  one  another  is  rather  thin. 

Approximately  at  the  place  where  it  turns  more  laterally  and  down- 
ward, the  facialis  canal  gives, off  from  its  antero-dorsal  parts  a  rather 
wide  branch  in  an  antero-dorsal  direction.  This  branch  (c.ophth.lat, 
Figs.  8,  10,  11;  PI.  XXIII;  PI.  XXV,  figs.  1-3)  soon  enters  the 
orbitotemporal  region,  ascending  there  after  a  short  distance  to  the 
dorsal  wall  and  continuing  forward  into  the  ethmoidal  region  rather 
close  below  the  upper  surface  of  this.  In  almost  the  whole  orbito- 
temporal region  and  throughout  the  ethmoidal  region  it  goes  rather 
straight  beneath  the  supra-orbital  sensory  canal  to  which  fine  rami  issue 
from  it  {rm.ophth.lat,  Pis,  XXI,  XXIII),  a  fact  which  fully  shows 
that  it  lodged  the  n.  ophthalmicus  lateralis.  It  may,  therefore,  properly 
be  called  the  canalis  n.  ophthalmici  lateralis.  In  the  subsequent  descrip- 
tion we  shall  return  to  it  and  its  importance  for  the  understanding  of 
the  trigemino- facialis  ganglionic  complex. 

Not  far  distally  of  the  canalis  n.  ophthalmici  lateralis,  a  second 
branch  issues  from  the  facialis  canal,  but  on  the  antero-ventral  side. 
This  branch  {c.bucc.lat,  Figs.  10,  11),  which  has  almost  the  same 
calibre  as  the  canalis  n.  ophthalmici  lateralis,  goes  forward  and 
opens  into  the  trigeminus  canal,  and,  as  the  trigeminus  and  facialis 
canals  lie  close  to  each  other  at  this  place,  it  is  rather  short.  As  will 
be  evident  from  my  subsequent  account  of  the  trigemino-facialis  gan- 
glionic complex,  the  canal  transmitted  certain  lateralis  fibres,  viz.,  those 
that  formed  the  n.  buccalis  lateralis. 

A  third,  wide,  but  short  branch  (c.pal1,  Figs.  10,  11)  is  given 
off  from  the  facialis  canal  close  to  the  external  opening.  This  branch 
runs  forward  to  the  postero-ventro-lateral  corner  of  the  orbit,  and, 
as  will  be  shown  below,  the  conditions  are  such  that  it  must  have  been 
pierced  by  the  r.  palatinus  facialis. 

It  has  already  been  pointed  out  above,  that  the  fine  but  pronounced 

1This  branch  was  discovered  by  preparation  after  the  photographs  had  been 
taken  and  is  therefore  not  shown  in  the  plates. 


Macropetalichthyids  and  other  Arthrodires — Stensio     109 

groove  s.ra,  along  the  ventral  border  of  the  external  (lateral)  surface 
of  each  lateral  wall  deepens  and  is  transformed  into  a  canal  a  short 
distance  anterior  to  the  external  opening  of  the  glossopharyngeus  canal, 
the  canal  arising  in  this  way  {era,  Figs.  1,  5,  7;  Pis.  XXI-XXIII) 
being  fairly  narrow.  Not  far  dorsally  of  this  canal  is  found  the 
posterior  opening  (ju2)  of  another  much  wider  canal  (ju,  Figs.  1, 
5.  7;  Pis.  XX-XXIII).  These  two  canals,  which  we,  after  their  index 
letters  in  the  previous  figures,  may  refer  to  as  era,  and  ju  respectively, 
go  forward  within  the  lateral  part  of  the  lateral  wall,  where  they  soon 
meet  and  join  to  a  wide  sinus  (si,  text  fig.  7;  Pis.  XXI-XXIII).  In 
this  sinus  there  may  be  distinguished  a  wide,  dorsal  division  correspond- 
ing to  the  canal  ju  and  a  narrow,  ventral  division  corresponding  to  the 
canal  era.  Although  very  imperfectly  separated  from  one  another, 
these  divisions  indicate  that  the  structures  traversing  the  two  canals  ju 
and  era,  retained  their  independence  and  original  positions  in  the 
sinus,  si. 

The  ventral  division  of  the  sinus  si,  is  continued  forward  by  a 
canal  which  is  lettered  ecom  in  the  figures  (Fig.  7;  Pis.  XXI, 
XXIII)  and  which  runs  in  an  anterior  and  slightly  medial  direction 
at  the  transition  between  the  lateral  and  ventral  walls  of  the  region. 
It  is  also  noteworthy  that  this  canal  (ecom)  has  a  very  superficial 
position,  as  it  is  situated  wholly  within  the  external  bone  layer.  After 
a  short  course  forward  it  divides  into  two  branches  of  about  equal 
calibre,  a  lateral  one  (ecar.ext)  and  a  medial  one  (ecar.int).  The 
former  of  these  runs  latero-dorsally  through  the  lateral  wall  and  opens 
close  to  and  postero-ventrally  of  the  facialis  canal  (Figs.  1,  7; 
Pis.  XXI,  XXIII),  while  the  latter  takes  a  course  forward  and  slightly 
medially  to  the  orbitotemporal  region.  The  former  of  these  branches 
is  throughout  its  extension  situated  within  the  external  bone  layer 
(Fig.  8),  as  is  also  the  latter  till  it  reaches  the  anterior  end  of 
the  orbitotemporal  region  (Fig.  8),  where  it  suddenly  leaves  the 
external  bone  layer  and  ascends  into  the  cartilaginous  interior  of  the 
ventral  wall  in  the  manner  that  will  be  described  below  in  the  account 
of  the  orbitotemporal  region.  As  we  shall  find  from  its  course,  the 
latter  branch  (ecar.int)  must  have  lodged  the  arteria  carotis  interna 
and  is  therefore  termed  the  internal  carotid  canal.  This  being  the 
case,  it  is  easy  to  understand  that  the  other  branch  (ecar.ext)  must 
have  been  traversed  by  the  arteria  carotis  externa.  (Cf.  Allis  1897, 
PP-  497-50O;  1908a;  1908b;  1909a,  pp.  51-55,  185-187;  1909b;  1911a; 
1911b;  1912a,  b,  c,  d;  1914a;  1914b;  1919a,  1922a,  pp.  266-268;  1922b; 
Allen  1905,  pp.  51-62;  Danforth  1912,  pp.  435-445;  Greil,  1913, 


1 10    Field  Museum  of  Natural  History — Geology,  Vol.  IV. 

PI.   LV,  fig.  2.)     Hence  this  may  properly  be  termed   the   external 
carotid  canal. 

The  branches  of  the  canal  c.com,  having  had  these  functions,  it  is 
evident  that  the  canal  c.com  itself  must  have  lodged  the  arteria  carotis 
communis.  From  the  canal  c.com,  the  arteria  carotis  communis  may 
have  continued  a  short  distance  backwards  into  the  ventral  division  of 
the  sinus  si,  there  probably,  as  we  shall  see,  having  received  the  arteria 
efferens  hyoidea  and  having  become  the  radix  aortae  (lateral  dorsal 
aorta).  The  radix  aortae  must  then  have  traversed  the  remaining  pos- 
terior part  of  the  ventral  division  of  the  sinus  si  behind  this,  continuing 
through  the  canal  era,  and  the  groove  s.ra,  to  the  anterior  end  of  the 
haemal  groove  (hczm).  At  the  anterior  end  of  this  it  probably  met  its 
fellow  of  the  opposite  side  and  joined  with  it  to  the  unpaired  aorta 
dorsalis,  which  in  its  backward  course  occupied  the  haemal  groove. 
The  efferent  arteries  from  the  two  or  three  anterior  branchial  arches 
may  probably  have  emptied  into  the  radix  aortae  of  their  side,  while 
those  from  the  remaining  posterior  branchial  arches  probably  opened 
into  the  anterior  portion  of  the  aorta  dorsalis.  My  view  concerning 
the  course  and  mutual  relations  of  the  arterial  trunks  mentioned  is 
further  elucidated  by  the  diagrammatic  sketch  reproduced  in  Fig.  6, 
and  as  is  evident  from  this  the  arterial  system  of  the  head  seems  to 


fend 


c.ophth.sup.V? 


cr.'ol 


V 


ju-i        c.hy      IX  S.ra, 

Fig.  5.    Macropetalichthys  rapheidolabis 


Primordial  neurocranium  in  lateral  view.  Occipital  region  after  specimens 
in  the  American  Museum,  New  York,  other  regions  after  a  specimen  in  Field 
Museum,  Chicago.    Bone  dark,  cartilage  dotted.    XH- 

a.opt,  division  of  the  distal  part  of  the  opticus  canal,  probably  for  the  arteria 
optica;  c.hy,  canal  for  the  v.  hyoidea;  c.ophth.sup.V ?,  canal  probably  for  the 
r.  ophthalmicus  superficialis  trigemini ;  cr.od,  crista  occipitalis  dorsalis ;  cr.ol, 
crista  occipitalis  lateralis ;  cr.sp,  cranio-spinal  process ;  /wi,  anterior  opening  of 
the  canal  ja.  The  opening  was  traversed  by  the  vena  mandiburalis ;  jui,  posterior 
opening  of  the  canal  ju;  na,  nasal  aperture;  orb,  orbit;  s.ra,  groove  for  the  radix 
aortae ;  vy,  canal  of  doubtful  importance ;  either  for  vessel  or  nerves  or  for 
both ;  II,  opticus  canal ;  IX,  glossopharyngeus  canal ;  Xvn,  canal  for  the  n.  vagus 
and  the  vena  cerebralis  posterior. 


Macropetalichthyids  and  other  Arthrodires — Stensio     III 

resemble  mostly  that  in  Chimcera  (Allis  1912a).  The  arteria  carotis 
interna  will  be  further  treated  below  in  the  description  of  the  orbito- 
temporal region. 

Turning  again  to  the  canal  ju,  we  find  that  anterior  to  the  sinus  si 
(Fig.  7;  Pis.  XXI,  XXIII)  it  takes  a  more  lateral  direction  than 
in  its  posterior  part.     It  opens  with  its  anterior  opening  (juy)  on  the 


L-— <z.pal 


cuc.int 


a.coru F^5f          \ 

..-a.effhy 

"  a  "rt"  ]^jfeS?N        -  'VJU 

—v.hy 

rSk\^z^ 

\     J$^<w\ ueffI 

i&  ^p  1       \ 

1                 1 

v.oerebr.jjost  ~ 

• 

u-dtors 
Fig.  6.    Macropetalichthys  rapheidolabis 

Diagrammatic  sketch  of  the  main,  arterial  and  venous  trunks  of  the  primordial 
neurocranium.  Outlines  of  neurocranium  in  ventral  view.  Arteries  red,  veins 
blue.  The  parts  of  the  different  vessels  situated  in  canals  or  cavities  indicated 
by  transversal  bands  of  color.     X/^. 

a.com,  arteria  carotis  communis;  a.c.ext,  arteria  carotis  externa;  a.c.int,  arteria 
carotis  interna;  a.eff.hy,  arteria  efferens  hyoidea;  a.effJ-a.eff.V,  efferent  arteries 
of  the  branchial  arches  I-V ;  a.dors,  aorta  dorsalis ;  a.pal,  possible  palatine  branch 
of  the  a.  carotis  interna ;  r.aort,  radix  aortae ;  v.cerebr.post,  vena  cerebralis  pos- 
terior; v.hy,  vena  hyoidea;  v.ju,  vena  jugularis;  v.m,  vena  mandibularis  (from 
the  dorsal  parts  of  the  mandibular  arch  to  the  jugular  vein). 


ii2    Field  Museum  of  Natural  History — Geology,  Vol.  IV. 

external  (lateral)  surface  of  the  lateral  wall  rather  close  laterally  to 
the  facialis  canal.  With  the  part  situated  anterior  of  the  sinus  si,  it 
joins  on  the  medial  side  a  fairly  wide  canal  jg,  which  comes  from  the 
postero-latero-ventral  corner  of  the  orbit,  perforating  in  its  course  back- 
wards the  ventral  portion  of  the  postorbital  process.  This  canal,  jg, 
does  not,  however,  run  straight^backwards  but  postero  latero-ventrally 
and  crosses  in  its  course  the  distal  part  of  the  facialis  canal  on  the 
dorsal  side.  Its  position  may  be  understood  from  PI.  XXI,  PI.  XXII, 
PI.  XXV,  figs,  i,  3,  and  Figs.  6,  7.  (In  PI.  XXIV  is  seen  a  section  of  it 
just  after  it  has  crossed  the  facialis  canal;  in  PI.  XXV,  fig.  1,  it  is 
seen  crossing  the  facialis  canal  on  the  dorsal  side,  and  it  is  also  obvious 
that  the  bone  layer  lining  it  is  continuous  proximally  with  the  part  of 
the  external  bone  layer  that  covers  the  posterior  surface  of  the  orbit; 
PI.  XXV,  fig.  3,  shows  the  same  part  of  it  as  the  preceding  figure  but 
from  behind.) 

From  the  conditions  in  recent  fishes  it  is  not  difficult  to  conclude 
what  the  functions  of  the  canals  ju  and  jg  were.  Both  must  have  been 
traversed  by  veins.  The  vein  that  traversed  the  canal  jg  evidently  col- 
lected the  blood  from  the  eye  bulb,  the  eye  muscles  and  probably  also 
from  the  anterior  parts  of  the  cavum  cerebrale  cranii.  Hence  it  must 
have  corresponded  to  the  vena  jugularis  interna  according  to  the 
terminology  mostly  employed  hitherto.  Allis  has,  however,  recently 
proposed  to  call  this  vein  simply  the  jugular  vein,  a  term  that  I  shall 
adopt  here  as  I  have  done  in  my  other  works.  (Cf.  Allen  1905,  pp. 
78-90,  PL  I,  figs.  1,  5;  PL  II,  figs.  13,  15;  PL  III,  figs.  23-25;  Allis 
1897,  pp.  500-506;  1903,  p.  93;  1908b,  pp.  219-222;  1909a,  pp.  40, 
45,  50,  187,  etc.;  1914a;  1914b;  1919a,  p.  222,  and  in  several  other 
places  throughout  the  paper;  1922a,  pp.  260-264;  1922b,  p.  153;  Greil 
1913,  PI.  54,  fig.  1 ;  PI.  55,  figs.  2,  8  (vena  capitis  lateralis)  ;  Grosser 
1907;  Lehn  1918,  pp.  365-372;  O'Donoghue  1914,  pp.  438-443,  an- 
terior cardinal  sinus  -f-  postorbital  sinus;  Parker,  T.  J.,  1887,  pp.  711- 
713;  Stensio  1921,  p.  178;  1923,  pp.  1244,  1260-1268;  1925.) 

A  vein  of  a  considerable  size  must  have  entered  the  canal  ju  through 
the  anterior  opening  ju±.  As  far  as  can  be  judged,  this  vein  collected 
the  blood  from  the  palatoquadrate  and  perhaps  also  from  certain  parts 
of  the  ethmoidal  region;  in  other  words,  it  seems  to  have  drained  a 
large  dorsal  part  of  the  mandibular  arch  and  nearest  surroundings. 
Hence  it  may  be  properly  termed  the  vena  mandibularis. 

The  vena  mandibularis  of  the  fish  so  defined,  after  a  short  passage 
backwards  within  the  canal  ju,  met  and  joined  the  jugular  vein  to  a 
common  large  stem  which  then  passed  backwards  through  the  dorsal 


Macropetalichthyids  and  other  Arthrodires — Stensio     113 

division  of  the  sinus  si  and  the  posterior  part  of  the  canal  ju  behind 
this  sinus,  then  continuing  along  the  external  surface  of  the  lateral 
wall  of  the  neurocranium  received  during  this  latter  part  of  its  course 
the  vena  cerebralis  posterior  as  it  passed  the  external  opening  of  the 
vagus  canal.  Despite  the  fact  that  the  vena  mandibularis  was  much 
larger  than  the  vena  jugularis,  the  common  stem  described,  that  arose 
by  its  confluence  with  the  latter,  must  for  morphological  reasons  be 
considered  as  the  backward  continuation  of  this,  and  hence  throughout 
its  extension  it  must  retain  the  name  of  jugular  vein.  The  course  and 
relations  of  the  juglar  vein,  the  mandibular  vein  and  the  vena  cerebralis 
posterior  seem  to  have  been  as  indicated  in  the  diagrammatic  sketch 
in  Fig.  6. 

In  the  dorsal  division  of  the  sinus  si — thus,  after  what  we  have 
just  found,  the  division  for  the  jugular  vein — there  opens  on  the  lateral 
side  a  short  but  rather  wide  canal  c.hy  (Figs.  1,  5,  7;  Pis.  XX- 
XXIII;  Pi.  XXIV,  figs.  1,  3),  which  leads  from  the  external  surface 
of  the  lateral  wall  of  the  region,  or,  to  define  it  more  closely,  from  the 
postero-dorsal  corner  of  the  anterior  part  of  the  posterior  field  of  the 
lateral  surface  of  the  region.  From  its  course  and  position  we  may 
conclude  with  a  rather  large  degree  of  probability  that  it  was  traversed 
by  a  vein.  This  supposed  vein  must  have  come  from  the  hyoid  arch 
and  emptied  into  the  jugular  vein,  thus  corresponding  partly  to  the 
sinus  hyoideus  of  Selachians.     I  call  it  here  the  vena  hyoidea. 

In  Selachians  the  sinus  hyoideus  is  a  large  vein  which  runs  upward 
on  the  posterior  side  of  the  hyoid  arch,  receiving  blood  not  only  from 
this  arch,  but  also  from  the  dorsal  and  middle  parts  of  the  mandibular 
arch  (Parker,  T.  J.,  1887,  PI.  35,  fig.  10;  O'Donoghue  1914,  pp.  441- 
442),  a  condition  which  explains  the  fact  that  a  mandibular  vein  is 
lacking.  In  Polypterus  a  hyoid  vein  seems  also  to  occur  (Allis  1922a, 
p.  264),  but  in  Ceratodus  (Greil  1913,  Pis.  54,  55)  and  the  Loricati 
(Allen  1905,  pp.  79-80),  the  dorsal  parts  of  this  vein  seem  to  be 
lacking.  At  least  in  the  Loricati  the  venous  blood  of  the  hyoid  arch 
goes  chiefly  forward  to  the  mandibular  vein,  arriving  through  this  into 
the  vena  jugularis.  In  Ceratodus  the  conditions  in  this  respect  are  not 
known  with  certainty.  The  venous  system  of  other  fishes  besides  those 
mentioned,  is  not  known  in  detail  and  accordingly  nothing  can  be  said 
of  the  veins  in  the  mandibular  and  hyoid  arches  there. 

The  occurrence  of  both  the  vena  mandibularis  and  the  vena  hyoidea 
in  Macropetalichthys  rapheidolabis  is,  it  seems  to  me,  to  be  considered 
a  primitive  character,  since  we  may  presume  that  the  venous  system 
of  fishes  originally  had  a  segmental  arrangement. 


ii4    Field  Museum  of  Natural  History — Geology,  Vol.  IV. 

If  the  interpretation  given  here  of  the  canal  c.hy  of  Macropetalich- 
thys  rapheidolabis  is  correct,  and  if  the  vena  hyoidea  during  the  passage 
to  this  canal  went  approximately  as  it  does  in  Selachians,  it  is  evident 
that  the  dorsal  end  of  the  hyoid  arch  must  have  articulated  against  the 
lateral  wall  of  the  region  anterior  to  the  external  opening  of  the  canal 
c.hy.  What  this  means  for  views  concerning  the  homologies  of 
the  hyomandibular  in  Selachians  and  Teleostomes  will  be  dealt  with 
below  in  the  account  of  the  visceral  skeleton.  It  has  been  mentioned 
above  that  the  arteria  efferens  hyoidea  ought  to  have  persisted  in 
M.  rapheidolabis,  and  if  so,  it  probably,  as  in  recent  fishes  in  which 
it  is  found,  went  upwards  along  the  posterior  side  of  the  hyoid 
arch  and  emptied  into  the  anterior  part  of  the  radix  aortae,  which,  as 
we  have  seen,  was  situated  here  within  the  sinus  si.  After  leaving  the 
hyoid  arch,  the  a.  efferens  in  order  to  reach  this  sinus  must  have 
entered  the  external  opening  of  the  canal  c.hy,  as  no  other  foramen 
can  be  found  for  it.  Perhaps  it  did  not,  however,  traverse  the  entire 
canal  c.hy,  but  took  near  the  proximal  end  of  this  a  more  anterior 
course,  entering  the  rather  fine  canal  c.ef  (Fig.  7;  Pis.  XX,  XXII), 
which,  at  least  on  the  left  side  of  the  Field  Museum  specimen,  runs 
from  the  proximal  part  of  the  canal  c.hy  forward,  medially  and  down- 
ward to  the  anterior  end  of  the  sinus  si.  If  well  arrived  into  the  sinus 
si  in  this  way,  the  artery  must  have  crossed  the  jugular  vein  and  passed 
downwards  to  the  ventral  division  of  the  sinus,  joining  there  the  radix 
aortae  at  the  transition  to  the  arteria  carotis  communis.  It  may,  how- 
ever, be  possible  that  the  canal  c.ef,  instead  of  being  traversed  by  the 
arteria  efferens  hyoidea,  as  here  supposed,  transmitted  the  truncus 
hyoideomandibularis  facialis,  and  if  this  was  the  case,  the  a.  efferens 
hyoidea  must  of  course  have  traversed  the  entire  canal  c.hy,  and  have 
entered  the  sinus  si  much  farther  back.  (Allen  1905,  pp.  44-62 ;  Allis 
1908a,  b;  1909a,  pp.  51-52,  183-184;  1909b;  1911a,  b;  1912a,  b,  c,  d; 
1922a,  pp.  264-268;  Danforth  1912,  pp.  435-445.) 

In  most  fishes  in  which  there  is  a  canal  for  the  jugular  vein  in 
the  lateral  wall  of  the  neurocranium,  the  jugular  vein  is  generally 
during  its  passage  through  this  canal  accompanied  for  some  distance 
by  the  truncus  hyoideomandibularis,  which  enters  the  canal  either  from 
in  front  through  the  anterior  opening  or  from  the  medial  side.  In 
the  former  case  the  truncus  hyoidemandibularis  has  its  exit  through 
the  cranial  wall  anterior  to,  in  the  latter  case  into  the  canal  for  the 
jugular  vein.  (Cf.  Allis  1897,  pp.  492-497;  1903,  pp.  87-95,  2^6; 
1908b,  pp.  219-222;  1909a,  pp.  44-45;  1911a,  p.  291;  1914a;  1914b; 


Macropetalichthyids  and  other  Arthrodires — StensiS     115 

19x9a;  1922a,  pp.  263-264;  1922b;  Lehn  1918,  pp.  363-372;  Pollard 
1892a,  PI.  30,  figs.  27-30;  Stensio  1921,  p.  178;  1923,  pp.  1244,  1261, 
1262-1268;  1925;  etc.) 

Concerning  M.  rapheidolabis ,  we  cannot  say  at  present  whether  the 
truncus  hyoidemandibularis  after  its  exit  from  the  facialis  canal  defin- 
itely left  the  cranial  wall  or  whether  it  again  entered  the  cranial  wall 
accompanying  the  vena  jugularis  for  some  distance.  If  the  former  of 
these  alternatives  were  true,  the  truncus  hyoidemandibularis  would  have 
left  the  cranial  wall  rather  far  anterior  of  the  hyoid  arch  and  would 
thus  have  reached  this  from  in  front  in  the  same  way  as  in  Selachians. 
(Cf.  Ruge  1897,  Figs.  3,  12,  13,  14;  Goodrich  1909,  Fig.  44;  Allis 
1915;  1918b;  cf.  also  van  Withe  1882,  PI.  15,  figs.  1,  3,  4,  6;  etc.) 
If,  on  the  other  hand,  the  latter  were  true,  it  is  at  once  evident  that  the 
truncus  hyoideomandibularis  cannot  have  entered  the  anterior  opening 
of  the  canal  jg  for  the  jugular  vein,  (as  we  have  found,  this  opening 
is  situated  in  the  orbit,  while  the  external  opening  of  the  facialis  canal 
lies  on  the  lateral  surface  of  the  lateral  wall  behind  the  orbit),  but 
would,  together  with  the  vena  mandibularis,  have  passed  through  the 
anterior  opening  (/*j)  of  the  canal  ju.  In  other  words,  the  truncus 
hyoideomandibularis  would,  with  this  alternative,  have  reached  the 
vena  jugularis  in  the  anterior  part  of  the  canal  ju,  after  traversing  the 
part  of  this  canal  situated  anterior  to  the  canal  jg. 

Assuming  that  it  did  so,  it  may  during  its  course  further  back- 
ward either  have  traversed  the  entire  dorsal  division  of  the  sinus  si 
and  behind  this  the  posterior  part  of  the  canal  ju,  or  may  soon  after  its 
entrance  in  the  sinus  si  have  turned  latero-dorsally,  entering  and 
traversing  the  canal  c.ef  and  the  distal  portion  of  the  canal  c.hy.  If 
it  took  the  former  of  these  courses  it  would  have  left  the  cranial  wall 
considerably  behind  its  arch,  the  hyoid  arch,  which,  as  we  have  seen, 
articulated  against  the  lateral  wall  of  the  region  anterior  to  the  external 
opening  of  the  canal  c.hy.  It  would  thus  have  gone  a  considerably 
roundabout  way  to  its  destination,  which  seems  rather  improbable.  If, 
on  the  contrary,  it  passed  from  the  sinus  si  through  the  canal  c.ef  and 
the  canal  c.hy,  it  would,  of  course,  have  had  its  exit  from  the  cranial 
wall  in  closer  relation  to  its  arch,  although  still  behind  this. 

The  conditions  on  the  external  surface  of  the  lateral  wall  of  the 
region  between  and  around  the  external  opening  of  the  facialis  canal 
and  the  anterior  opening  of  the  canal  ju,  would,  perhaps,  if  they  were 
known  in  detail,  enable  us  to  decide  with  considerable  degree  of 
probability  what  course  the  truncus  hyoideomandibularis  took  after 


n6    Field  Museum  of  Natural  History — Geology,  Vol.  IV. 

leaving  the  facialis  canal1.  But,  unfortunately,  the  external  surface  of 
the  wall  is  not  sufficiently  well  preserved  to  enable  me  to  determine 
this  in  any  of  the  specimens  so  far  investigated  by  me. 

In  dealing  with  the  trigeminus  and  facialis  canals  below  we  shall 
see  that  the  r.  oticus  lateralis  must  have  originated  in  the  proxifnal  part 
of  the  facialis  canal,  which  it  ""left  either  through  the  external  opening, 
or  through  a  canal  of  its  own.  In  the  latter  case  it  would  have  issued 
from  the  dorsal  side  of  the  distal  part  of  the  facialis  canal.  A  few 
fine  canals,  which  were  traversed  by  rami  from  the  r.  oticus  lateralis  to  a 
sensory  canal  portion  in  the  dermal  cranial  roof  are  seen  in  the  Field 
Museum  specimen  (in,  Pis.  XX,  XXII).  These  fine  canals  could, 
however,  not  be  traced  downwards  to  their  origin,  and,  therefore,  we 
cannot  say  whether  they  come  from  a  larger  canal  within  the  cranial 
wall  or  whether  each  of  them  went  independently  down  and  opened  on 
the  lateral  surface  of  the  lateral  wall. 

Labyrinth  Cavity 

The  labyrinth  cavity  is  completely  preserved  only  in  the  Field 
Museum  specimen.  Traces  of  it  are,  however,  seen  also  in  one  of  the 
New  York  specimens  (PL  XXVII).  It  (lab.cav,  Fig.  4;  PL  XX;  PL 
XXVI,  figs.  3,  4;  PI.  XXVII)  is  large  and,  as  pointed  out,  lined 
throughout  by  a  thin  layer  of  perichondral  bone,  the  labyrinth  bone 
layer.  As  has  also  been  mentioned,  it  is  completely  separated  from  the 
cavum  cerebrale  cranii  by  a  thick  septum  (PL  XX)  which  consisted 
of  cartilage  lined  by  the  labyrinth  bone  layer  on  the  labyrinth  side  and 
by  the  internal  bone  layer  on  the  cerebral  side. 

The  division  for  the  sacculus  (sac,  PL  XXVI,  fig.  3)  is  not  well 
exposed,  but,  as  far  as  can  be  judged,  it  cannot  have  been  very  large. 
It  is  not  distinctly  separated  from  the  remaining  divisions  of  the 
cavity.  From  its  dorsal  part  a  canal  (d.end,  Fig.  4;  PL  XX; 
PL  XXVI,  fig.  3)  issues  in  a  dorso-postero-lateral  direction  to  the 
dorsal  surface  of  the  primordial  neurocranium.  This  canal  seems, 
however,  to  end  some  distance  below  the  dermal  bones  of  the  cranial 
roof,  a  fact  which  probably  indicates  that  the  cartilage  at  this  place 
did  not  reach  quite  up  to  the  dermal  bones,  i.e.,  that  there  probably 
was  a   shallow   fossa   into   which  the   canal   had   its   dorsal   opening 

1  The  presence  of  a  groove  between  the  two  openings  would  of  course  have 
indicated  that  the  r.  hyoideomandibularis  after  its  exit  from  the  facialis  canal 
went  backward  along  the  lateral  surface  and  entered  the  canal  ju  through  the 
anterior  opening  j'ih.  The  absence  of  such  a  groove  would  of  course  point  in 
the  opposite  direction.  If  the  two  openings  should  be  found  situated  in  a  com- 
mon pit  this  must  probably  also  indicate  that  the  tr.  hyoideomandibularis  entered 
the  canal  ju  through  the  anterior  opening  jui. 


Macropetalichthyids  and  other  Arthrodires — Stensio     117 

(Fig.  3;  Pis.  XIX,  XX).  From  its  course  and  relations  it  is  evi- 
dent that  the  canal  in  question  must  have  lodged  the  ductus  endo- 
lymphaticus,  which,  accordingly,  opened  on  the  dorsal  surface  of  the 
primordial  neurocranium  in  a  fossa  endolymphatica  as  in  Selachians 
(Retzius  1881). 

Slightly  postero-ventrally  of  the  canal  for  the  ductus  endolym- 
phaticus,  another,  but  much  wider  canal,  issued  from  the  division  for 
the  sacciilus.  This  canal  (v.lb,  Figs.  10,  11 ;  PI.  XX;  PI.  XXIV, 
fig.  2;  PI.  XXV,  figs.  1,  2;  PI.  XXVI,  figs.  1,  2,  3),  which  runs  back- 
ward and  somewhat  dorsally  to  the  dorsal  division  of  the  vagus  canal, 
has  already  been  described  in  another  connection,  and,  as  pointed  out 
there,  it  probably  transmitted  a  large  vein,  that  drained  the  whole,  or 
at  least  the  main  part,  of  the  labyrinth. 

The  division  for  the  utriculus  (utr,  PI.  XX;  PI.  XXVI,  figs.  3,  4) 
appears  to  be  relatively  very  large,  but  as  it  is  not  distinctly  marked 
off  from  the  other  divisions,  its  size  may,  perhaps,  be  'over-estimated. 
As  is  seen  from  the  plates,  its  largest  extension  is  from  above  down- 

VII      c.car.ext 

19      \  ! 


Fig.  7.    Macropetalichthys  rapheidolabis 

Diagrammatic  sketch  showing  the  position  of  certain  canals  in  the  lateral 
wall  of  the  labyrinth  region.  Certain  ventral  parts  of  the  lateral  wall  removed. 
Bone  layers  indicated  with  shading  and  when  in  cross  section  with  black  lines. 
Cartilage  dotted.    XH- 

c.com,  canal  for  the  arteria  carotis  communis ;  c.ef,  canal  perhaps  for  the 
arteria  efferens  hyoidea ;  c.hy,  canal  for  the  vena  hyoidea ;  era,  canal  for  the 
radix  aortse  behind  the  sinus  si:  jg,  canal  for  the  vena  jugularis  through  the 
postorbital  process;  ju,  canal  behind  jg,  for  the  vena  jugularis,  anterior  of  jg, 
for  the  vena  mandibularis  jui,  pit,  anterior  and  posterior  openings  of  the  canal  ju ; 
si,  sinus  arisen  by  confluence  of  the  canals  ju  and  era;  s.ra,  groove  for  the 
radix  aorta  (lateral  dorsal  aorta);  VII,  canal  for  the  n.  facialis;  IX,  canal  for 
the  n.  glossopharyngeus. 


n8     Field  Museum  of  Natural  History — Geology,  Vol.  IV. 

wards  and  forwards,  which  must  mean  that  the  utriculus  did  not  have 
a  horizontal  position,  but  was  inclined  in  the  same  way  as  in  Selachians 
(cf.  Retzius  1881).  Just  at  the  antero-ventral  end,  there  is,  immedi- 
ately anterior  of  the  place  of  entrance  of  the  acusticus  canal  (VIII) 
a  rather  pronounced  bulge  (ru,  PI.  XXVI,  fig.  3),  which,  to  judge 
from  its  position,  probably  contained  the  recessus  utriculi.  Immedi- 
ately in  front  of  this  bulge  lies  the  proximal  portion  of  the  facialis 
canal  (VII). 

The  divisions  for  the  semicircular  canals  are  very  imperfectly 
known,  which  is  due  partly  to  the  fact  that  they  could  not  be  laid 
bare  without  danger  to  other  important  structures,  and  partly  to  the 
circumstance  that  they  probably  are  not  well  differentiated  from  the 
other  parts  of  the  labyrinth  cavity.  It  seems,  however,  not  unlikely 
that  the  part  designated  with  the  letters  c.sem.ant,  in  PI.  XX  and  PI. 
XXVI,  figs.  3,  4,  was  occupied  by  the  canalis  semicircularis  anterior, 
and  if  this  is  true  the  canalis  semicircularis  anterior  would  have  had 
a  position  almost  transversal  to  the  longitudinal  axis  of  the  head.  This 
position  would,  as  is  easily  understood,  have  been  caused  by  the  back- 
ward shifting  of  the  orbit.  What  parts  of  the  divisions  for  the  other 
two  semicircular  canals  are  represented  by  the  fragments  denoted  by 
c.sem  in  PI.  XXI  and  PI.  XXVI,  fig.  4,  is  difficult  to  say  with  cer- 
tainty, but  at  least  what  is  seen  in  PI.  XXI  seems  most  probably  to 
be  a  part  of  the  division  for  the  canalis  semicircularis  externus,  which 
thus  would  have  been  situated  as  in  Elasmobranchs. 

The  n.  acusticus,  as  is  seen  from  the  position  of  its  canal  (VIII), 
enters  the  labyrinth  cavity  at  the  very  bottom,  as  in  certain  Elasmo- 
branchs (Scyllicum,  Raja,  cf.  Retzius  1881),  and  is  rather  short. 
The  glossopharyngeus,  as  has  already  been  mentioned,  traversed  the 
postero-ventral  parts  of  the  labyrinth  cavity.  The  facialis  went  first 
for  some  distance  along  the  antero-ventro-medial  part  of  the  labyrinth 
cavity,  then  turned  laterally  and  passed  along  the  antero-ventral  part 
of  the  same  cavity  between  it  and  the  orbit.  (PI.  XXV,  figs.  1,  3; 
PI.  XXVI,  figs.  3,  4.) 

From  the  description  now  given  of  the  labyrinth  cavity  it  seems 
rather  probable  that  this  was  larger  than  the  membranous  labyrinth  en- 
closed in  it,  a  condition  which  makes  it  difficult  to  conclude  anything 
with  certainty  about  the  finer  details  of  the  latter.  But  what  is,  how- 
ever, known  so  far  of  the  larger  divisions  of  the  labyrinth  cavity, 
indicates  beyond  doubt,  as  we  have  seen,  that  the  membranous  labyrinth, 
at  least  in  certain  of  its  general  characters,  was  of  the  Elasmobranchian 
type. 


Macropetalichthyids  and  other  Arthrodires — Stensio     119 

A  more  detailed  knowledge  of  the  labyrinth  cavity  would  seem  evi- 
dently to  be  of  great  importance  for  the  understanding  of  the  affinites 
of  Macropetalichthys  to  other  fishes,  and  it  is  therefore  to  be  hoped 
that  new  material,  fit  for  a  detailed  investigation  of  the  labyrinth 
cavity,  will  soon  be  found. 

Orbitotemporal  Region 

The  orbitotemporal  region  (Figs.  1,  3,  5,  8;  Pis.  XIX-XXIII;  PI. 
XXIV,  fig.  1 ;  PI.  XXV,  figs.  1,  2;  PI.  XXVI,  figs.  1,  2)  is  strikingly 
short  and  broad,  its  breadth  being  almost  three  times  as  great  as  its 
length.  The  breadth  is,  however,  much  greater  at  the  bottom  of  the  re- 
gion than  higher  up,  a  condition  which  is  caused  by  the  presence  of  the 
very  extensive  floors  for  the  orbits  (Figs.  3,  8;  Pis.  XIX,  XXI,  XXIII). 
The  height  is  greatest  at  the  posterior  end  of  the  region,  where  it  is 
about  equal  to  the  length  and  a  third  of  the  breadth,  decreasing  slowly 
and  gradually  forwards  throughout  the  region.  On  account  of  the  orbital 
floors,  the  region  is,  at  the  bottom,  not  marked  off  from  the  adjacent 
regions,  otherwise  being,  however,  considerably  narrower  than  these. 

The  orbitae  are  rather  small  and  lie  far  apart.  While  in  Arthrodires 
in  general  they  are  situated  fairly  far  forward,  and  have  the  entrances 
facing  almost  straight  laterally,  they  have  here  shifted  a  certain  dis- 
tance in  a  postero-medial  direction  and  have  their  entrances  directed 
much  upwards  (Figs.  3,  5,  8;  Pis.  XIX,  XX;  PI.  XXIV,  fig.  1). 
On  account  of  the  shifting,  they  are  much  more  completely  bounded 
by  the  primordial  neurocranium  than  is  generally  the  case  in  fishes, 
for,  in  fact,  they  have  not  only  a  medial,  a  posterior  and  an  anterior, 
but,  in  addition,  a  ventral  and  to  a  large  extent  a  lateral  wall  formed 
by  this.  The  ventral  wall,  which  has  been  already  referred  to  as  the 
orbital  floor,  is  a  rather  thin  plate  which  is  continuous  laterally  and 
posteriorly  with  the  postorbital  process,  medially  with  the  ventral  part 
of  the  interorbital  wall  and  anteriorly  with  the  ethmoidal  region.  It 
consists  of  cartilage  covered  both  on  the  upper  (orbital)  and  lower 
surfaces  by  the  external  bone  layer.  The  lateral  wall,  as  far  as  it  is 
present,  is  formed  by  the  large  postorbital  process,  which  reaches  so 
far  forward  that  it  leaves  only  a  rather  limited  opening  between  its 
anterior  end  and  the  ethmoidal  region  (Figs.  3,  5;  Pis.  XIX,  XX; 
PI.  XXIV,  fig.  1).  A  transverse  section  through  the  posterior  half  of 
the  region  that  shows  the  relations  between  the  different  walls  of  the 
orbit  at  this  place  as  well  as  the  shape  of  the  orbit  itself  is  seen  in 
Figure  8.     The  orbital   entrance  is  of   an   elliptical   shape,  with  the 


120    Field  Museum  of  Natural  History — Geology,  Vol.  IV. 

largest  axis  directed  so  as  to  converge  a  little  towards  that  of  the  other 
side  in  a  postero-dorso-medial  direction  (Fig.  3;  Pis.  XIX,  XX; 
PI.  XXIV,  fig.  1). 

For  detailed  description  we  may  consider  the  region  to  be  com- 
posed of  four  walls — a  ventral,  a,  dorsal,  and  a  right  and  a  left  lateral 
— all  of  which,  of  course,  are  continuous  with  the  correspondingly 
situated  walls  in  the  adjacent  regions. 

The  ventral  wall  (Figs.  1,  5,  8;  Pis.  XXI,  XXII,  XXIII;  PI. 
XXV,  figs.  1,  2;  PI.  XXVI,  figs.  1,  2)  is  characterized  in  the  first 
place  by  its  very  considerable  breadth,  which  remains  almost  unchanged 
throughout  the  region.  As  a  whole  it  is  thin,  and  especially  is  this 
the  case  in  the  lateral  (orbital  floors)  and  median  parts.  Like  the 
corresponding  walls  in  the  adjacent  regions,  it  is  covered  by  the  inter- 
nal bone  layer  dorsally  and  the  external  bone  layer  ventrally  and  is 
curved  so  that  the  ventral  surface  is  concave  in  transversal  direction. 
It  has  no  fenestra  hypophyseus  or  fenestration  whatever  and  the  fossa 
hypophyseus  is  only  very  slightly  developed  on  its  dorsal  (cerebral) 
side. 

The  canal  for  the  internal  carotid  artery  of  each  side  (c.car.int, 
Fig.  8;  Pis.  XXI-XXIII;  PI.  XXV,  fig.  2)  enters  the  ventral  wall 
of  the  region  from  behind  and  perforates  the  lateral  part  of  this  that 
forms  the  orbital  floor.  Its  direction  is  forward  and  a  little  medially 
and,  in  the  posterior  larger  part  of  its  course,  it  is  here,  as  in  the 
labyrinth  region,  situated  entirely  within  the  external  bone  layer,  thus 
very  superficially.  In  the  anterior  part  of  the  region  it  penetrates 
deeper  into  the  wall,  curving  postero-dorso-medially.  With  this  latter 
course  it  arrives  up  and  into  the  lateral  wall  of  the  region,  where  it 
finally  opens  into  the  opticus  canal  (PI.  XXIII;  PI.  XXV,  fig.  2),  its 
opening  into  this  being  situated  on  the  anterior  side  close  to  the  orbit. 
Just  at  the  place  where  it  curves  from  the  anterior  to  the  postero- 
dorso-medial  direction,  it  lies  somewhat  anterior  of  the  orbit,  thus 
really  in  the  basal  part  of  the  antorbital  process,  a  fact  which  is  cer- 
tainly explained  by  the  backward  shifting  of  the  orbits.  We  shall  have 
the  opportunity  of  returning  to  it  again  in  connection  with  the  de- 
scription of  the  opticus  canal. 

The  orbital  floor  of  each  side  is  perforated  by  a  second  canal  (c.pal2, 
Pis.  XXI,  XXII)  which  begins  in  the  orbit  and  runs  antero-ventrally 
through  the  floor,  opening  into  the  anterior  portion  of  the  suborbital 
part  of  the  internal  carotid  canal.  At  the  place  where  the  latter  canal 
curves  dorso-postero-medially  it  has  an  opening  (c.pal3,  Fig.  1), 
leading  to  the  ventral   surface   of   the   neurocranium,  and    from   this 


Macropetalichthyids  and  other  Arthrodires — Stensio     121 

opening  a  shallow  groove  (s.  pal,  Fig.  i)  goes  forward.  As  we 
shall  see  from  the  description  of  the  trigemino-facialis  ganglionic 
complex  below,  it  is  not  difficult  to  conclude  that  the  canal  c.pal2  was 
traversed  by  the  r.  palatinus  facialis,  which  passed  down  to  the  anterior 
portion  of  the  suborbital  part  of  the  internal  carotid  canal,  then  left 
this  and  arrived  at  the  ventral  side  of  the  neurocranium  by  the  open- 
ing c.pd3. 

The  dorsal  wall  (Figs.  3,  8;  Pis.  XIX,  XX;  PI.  XXIV,  fig.  1; 
PI.  XXV,  figs.  1,  2;  PI.  XXVI,  figs.  1,  2)  is  broad  and  short  like  the 
ventral  one,  but  on  the  other  hand  considerably  thicker.  As  far  as  one 
can  judge  from  its  appearance  in  the  fossil  it  had  no  fontanelle,  and, 
as  already  ^pointed  out,  it  is  devoid  of  the  external  bone  layer.  Its 
upper  (external)  surface  is  slightly  convex  in  transversal  direction 
and  provided  with  grooves  for  the  ridges  on  the  lower  side  of  the 
dermal  bones  in  which  the  sensory  canals  are  enclosed.  In  its  anterior 
part  it  is,  as  already  mentioned  above,  traversed  by  the  canal  for  the 
n.  ophthalmicus  lateralis,  which  arrives  there  from  below  from  the 
lateral  wall.  Otherwise  there  are  in  it  only  several  very  fine  canals, 
the  most  important  of  which  issue  from  the  canal  for  the  n.ophthalmi- 
cus  lateralis  and  pass  upwards  to  the  supraorbital  sensory  canal. 

Finally,  the  lateral  walls  (Figs.  1,  5,  8;  Pis.  XXII-XXIV;  PI. 
XXV,  figs.  1,  2;  PI.  XXVI,  figs.  1,  2),  although  thick,  are  by  no  means 
as  thick  as  those  in  the  labyrinth  region.  Their  thinnest  place  is  situated 
around  the  opticus  canal  (II).  They  are  covered  both  by  the  internal 
and  external  bone  layers.  Their  external  surface  is  concave  both  in 
dorso-ventral  and  antero-caudal  direction.  Their  internal  surface  has 
a  rather  complicated  appearance,  as  may  be  understood,  from  the  figures 
quoted  and  as  will  be  further  dealt  with  below. 

Each  lateral  wall  is  perforated  by  several  canals.  We  begin  here 
with  the  most  posterior  one,  the  trigeminus  canal,  proceeding  forward 
from  this. 

The  trigeminus  canal  (V,  V2,3,  Figs.  10,  11;  PI.  XXIII;  PI. 
XXV,  figs.  1,  2;  PI.  XXVI,  figs.  1,  2)  leaves  the  cavum  cerebrale 
cranii  a  short  distance  anterior  to  the  facialis  canal  and,  as  pointed  out 
above,  its  internal  opening  has  nothing  to  do  with  the  acustico- facialis 
recess.  It  runs  antero-laterally  and  somewhat  ventrally  to  the  postero- 
ventro-medial  corner  of  the  orbit,  and,  on  account  of  the  fact  that  the 
cranial  wall  is  much  thinner  at  this  place  than  immediately  behind  the 
orbit,  it  naturally  becomes  considerably  shorter  than  the  facialis  canal. 
The  external  opening,  as  is  easily  understood,  is  situated  rather  far 
medially  of  that  of  the  facialis  canal. 


122     Field  Museum  of  Natural  History — Geology,  Vol.  IV. 

In  the  trigeminus  canal  there  may  properly  be  distinguished  two 
parts,  a  proximal  short  and  wide  one  (V)  and  a  distal  rather  long 
and  narrower  one  (V2,3),  the  former  of  which  actually  forms  a  recess 
on  the  lateral  side  of  the  cranial  wall,  a  recess  which  may  be  called 
the  trigeminus  recess. 

From  the  antero-dorsal  part  of  the  trigeminus  recess,  as  thus  de- 
fined, there  issues  a  rather  wide  canal  (c.ophth.sup.V)  which  runs  for- 
ward and  a  little  upward,  crossing  the  canal  for  the  n.  ophthalmicus 
lateralis  (c.ophth.lat)  on  the  ventro-medial  side  and  opening  into  the 
postero-ventro-medial  part  of  the  orbit  (PI.  XXIII;  PI.  XXV,  fig.  2; 
PI.  XXVI,  figs.  1,  2).  Slightly  ventrally  of  this  canal  a  second,  but 
considerably  narrower  one,  (c.ophth.prof),  leaves  the  trigeminus  re- 
cess, and  taking  its  course  ventro-medially  of  the  canal  for  the  n.  oph- 
thalmicus lateralis,  goes  almost  straight  forward  to  the  orbit,  where  it 
opens  somewhat  postero-ventrally  of  the  former. 

With  the  knowledge  we  now  possess  of  the  conditions  in  recent 
fishes,  it  is  easy  to  conclude  what  the  functions  of  the  canals  just  de- 
scribed were,  and,  in  addition,  to  make  out  to  a  certain  degree  how 
the  trigemino-facialis  ganglionic  complex  and  its  roots  were  developed. 
For  comparison  the  reader  may  be  referred  to  the  works  of  Herrick 
(1899;  1900;  1901),  Johnston  (1898;  1901),  Kingsbury  (1897), 
Allis  (1897;  1901 ;  1903;  1909a;  1918c;  1922),  Landacre  (1916), 
Norris  and  Hughe  (1920)  and  Strong  (1895),  etc. 

As  mentioned  in  another  connection,  it  is  fully  evident  that  the 
canal  designated  by  the  letters  c.opht.lat  transmitted  the  n.  ophthalmicus 
lateralis  (cf.  above)  and  as  this  canal  does  not  communicate  with  the 
trigeminus  canal  or  the  fine  canals  issuing  from  the  latter,  we  may  also 
conclude  with  full  certainty  that  it  did  not  give  passage  to  any  general 
cutaneous  fibres.  These  fibres  to  the  orbit  or  dorsal  side  of  the  neu- 
rocranium  must  therefore  undoubtedly  have  emerged  into  the  orbit 
through  the  canals  c.ophth.prof  and  c.ophth.sup.V,  and  it  is  easy  to 
understand  that  those  of  them  which  passed  through  the  canal  c.ophth. 
prof  formed  the  r.  ophthalmicus  profundus  trigemini,  or  a  somewhat 
equivalent  nerve,  while  the  others  which  passed  through  the  canal 
c.ophth.sup.V  formed  the  r.  ophthalmicus  superficialis  trigemini.  In 
other  words,  the  general  cutaneous  fibres  which  formed  the  r.  ophthal- 
micus profundus  were  transmitted  to  the  orbit  through  the  canal  c.ophth.- 
prof, and  those  which  formed  the  r.  ophthalmicus  superficialis  trigemini 
through  the  canal  c.ophth.sup.V ,  while  the  lateralis  fibres  which  formed 
the  n.  ophthalmicus  lateralis  never  entered  the  orbit  but  passed  in  the 
interorbital  wall  through  a  canal  of  their  own  which  is  given  off  from 


Macropetalichthyids  and  other  Arthrodires — Stensio     123 

the  facialis  canal  and  has  no  connection  with  the  trigeminus  canal-  (in- 
cluding the  trigeminus  recess).  A  separate  course  of  the  r.  ophthalmi- 
cus lateralis  and  r.  ophthalmicus  profundus  trigemini  is,  besides  in  the 
form  now  under  consideration,  found  in  Acipenscr,  Polyodon  (Stensio 
1925),  Saurichtliys  (Stensio  1925)  and  Siluroids  (Workman  1900, 
pp.  403-407;  Herrick  1901,  pp.  201-203). 

The  r.  ophthalmicus  superficialis  trigemini  and  the  r.  ophthalmicus 
profundus  trigemini  having  issued  from  the  trigeminus  recess — the 
proximal  part  of  the  trigeminus  canal — it  is  fully  evident  that  this 
recess  must  have  contained  at  least  the  main  parts  of  the  ganglion 
gasseri  and  the  profundus  ganglion,  i.e.,  the  main  parts  of  the  ganglia 
of  the  general  cutaneous  fibres.  Only  small  parts  of  these  ganglia 
may  perhaps  have  reached  into  the  cavum  cerebrale  cranii.  From  the 
origin  of  the  r.  ophthalmicus  superficialis  and  the  r.  ophthalmicus  pro- 
fundus trigemini,  we  can  further  conclude  that  the  distal  narrower 
part  of  the  trigeminus  canal  (V2,3)  transmitted  the  r.  maxillaris  and 
the  r.  mandibularis  trigemini  after  their  origin  from  the  ganglion 
gasseri.  That  these  two  latter  rami  were  accompanied  by  certain 
lateralis  fibres  and  perhaps  also  by  certain  communis  fibres,  we  shall  see 
from  the  subsequent  account. 

During  their  passage  through  the  cranial  wall,  the  trigeminus  roots 
proper  (i.e.,  the  general  cutaneous  roots  and  the  motor  root)  of  recent 
fishes  are,  as  a  rule,  accompanied  by  a  lateralis  root,  which  leaves  the 
medulla  oblongata  postero-dorsally  of  the  trigeminus  root  proper  run- 
ning outward  postero-dorsally  or  dorsally  of  these,  and  having  its 
ganglion  dorsally  or  postero-dorsally  of  the  ganglion  gasseri.  From 
the  ganglion  of  this  lateralis  root  the  n.  ophthalmicus  lateralis  and 
n.  buccalis  lateralis  take  their  origin. 

In  Macropetalichthys  rapheidolabis,  in  which  the  canal  for  the 
n.  ophthalmicus  lateralis  issues  from  the  facialis  canal  and  in  which, 
as  we  have  seen,  there  is  no  communication  between  the  proximal 
parts  of  the  latter  canal  and  the  trigeminus  canal,  the  lateralis  root 
which  gave  rise  to  the  n.  ophthalmicus  lateralis  and  the  n.  buccalis 
lateralis  must  evidently  have  left  the  cranial  cavity  through  the  facialis 
canal,  traversing  the  proximal  part  of  this  canal  and  having  its  ganglion 
there.    The  n.  buccalis  lateralis  thus  also  arose  within  the  facialis  canal. 

In  order  to  reach  the  trigeminus  canal,  the  n.  buccalis  lateralis  in 
M.  rapheidolabis  must,  soon  after  its  origin,  have  turned  forward, 
traversing  the  short  canal  c.buc.lat,  described  above  (Figs.  10,  11), 
which  leaves  the  facialis  canal  slightly  distally  and  somewhat  ven- 
trally  of  the  canal  for  the  n.  ophthalmicus  lateralis  and  goes  to  the 


124    Field  Museum  of  Natural  History — Geology,  Vol.  IV. 

distal  narrow  part  (V2,3)  of  the  trigeminus  canal.  The  n.  buccalis 
lateralis  after  arriving  into  this  part  of  the  trigeminus  canal,  probably 
joined  more  or  less  intimately  the  r.  maxillaris  trigemini  and  passed 
distally  with  this  in  the  normal  way. 

From  the  considerations  given  the  following  is  evident  in  M. 
rapheidolabis  concerning  the  trigemino-facialis  ganglionic  complex  and 
its  roots :  i .  Into  the  trigeminus  recess  there  entered  only  the  general 
cutaneous  roots  and  the  viscero-motor  root  of  the  mandibular  arch. 
2.  The  ganglion  gasseri  and  the  profundus  ganglion  must  have  been 
situated  in  a  proximal  wide  part  of  the  trigeminus  canal,  called 
here  the  trigeminus  recess.  3.  Into  the  facialis  canal  there  entered  all 
the  lateralis  fibres  and  all  the  communis  fibres  of  the  ganglionic  com- 
plex and,  further,  the  viscero-motor  root  of  the  hyoid  arch.  4.  The 
ganglia  of  the  fibres  entering  the  facialis  canal,  i.e.,  in  this  case  the 
ganglion  geniculi,  the  ganglion  of  the  dorsal  lateralis  root  and  the 
ganglion  of  the  ventral  lateralis  root,  must  have  been  situated  in  the 
proximal  part  of  this  canal  and  partly,  perhaps,  in  the  acustico-facialis 
recess. 

The  lateralis  ganglion  of  the  dorsal  lateralis  root  (from  which  the 
n.  ophthalmicus  lateralis  and  n.  buccalis  lateralis  arose)  must  in  the 
facialis  canal  have  had  its  position  antero-dorsally  of  the  two  other 
ganglia,  the  ganglion  geniculi  and  the  ganglion  of  the  ventral  lateralis 
root.  Although  separated  from  the  ganglion  gasseri  by  a  rather  thick 
wall,  it  thus  had,  as  far  as  can  be  judged,  about  its  normal  position  in 
relation  to  this,  and  the  fact  that  it  was  situated  in  the  facialis  canal 
is  therefore  of  hardly  any  importance  from  a  morphological  point  of 
view.  Similar  arrangements  would  certainly  arise  in  many  recent  forms 
if  the  septa  of  connective  tissue  that  there  more  or  less  completely 
separate  the  ganglia  in  question  and  their  roots  from  each  other 
developed  more  strongly  and  chondrified  or  ossified.  Moreover,  we 
find  in  certain  recent  forms  that  ail  the  roots  of  the  trigemino-facialis 
ganglionis  complex  may  run  close  together  through  a  single  canal  in 
the  cranial  wall,  and  that  their  ganglionic  formations  may  be  very 
intimately  connected  with  each  other.  Thus  the  wall  between  the 
trigeminus  and  facialis  canals  in  certain  cases  is  reduced.  That  varia- 
tions occur  within  certain  bounds  in  the  trigemino-facialis  ganglionic 
complex  of  fishes  is  accordingly  not  so  remarkable. 

Whether  in  M.  rapheidolabis  any  general  cutaneous  fibres  went 
backward  to  the  facialis  branches  and  any  communis  fibres  forward 
to  the  trigeminus  branches  it  is  not  possible  to  say  with  certainty  from 
the  conditions  in  this  fossil,  but  it  is  not  impossible  that  this  was  the 


Macropetalichthyids  and  other  Arthrodires — Stensio     125 

case,  for  these  fibres  can  very  well  be  thought  to  have  traversed  the 
canal  c.buc.Iat.  Possible  communis  fibres  to  the  n.  ophthalmicus  lateralis 
must  have  entered  the  canal  for  this  nerve  directly  from  the  facialis 
canal. 

The  r.  oticus  lateralis,  which,  as  is  known,  is  a  branch  from  the 
n.  buccalis  lateralis,  certainly  arose  within  the  facialis. canal,  probably 
just  as  the  n.  buccalis  lateralis  on  its  way  forward  entered  the  canal 
c.buc.Iat.  Whether  the  r.  oticus  lateralis  then  traversed  the  entire  re- 
maining part  of  the  facialis  canal  or  sooner  or  later  perforated  its 
dorsal  wall,  entering  a  canal  of  its  own,  it  is  impossible  to  decide  at 
present. 

Apart  from  the  r.  oticus  facialis,  the  distal  part  of  the  facialis 
canal  (distally  of  the  point  of  origin  of  the  ophthalmicus  lateralis 
canal)  transmitted  communis  fibres — the  viscero-motor  fibres — for  the 
hyoid  arch,  lateralis  fibres  for  the  n.  mandibularis  externus  and  pos- 
sibly also  a  few  general  cutaneous  fibres.  All  these  fibres  formed  to- 
gether a  large  facialis  stem  which,  soon  after  its  origin  from  the 
ganglia  within  the  canal,  must  have  branched  into  the  r.  palatinus  and 
the  truncus  hyoidemandibularis. 

The  r.  palatinus,  after  its  origin  in  the  facialis  canal,  must  first 
have  turned  forward  and  traversed  the  canal  c.palx  which  leads  from 
the  facialis  canal  to  the  orbit  (cf.  above).  Well  within  the  orbit  the 
nerve  continued  forward  for  some  distance  in  a  groove  on  the  orbital 
floor,  then  penetrated  downwards  in  the  floor  through  the  canal 
c.pal2  to  the  suborbital  part  of  the  internal  carotid  canal.  In  the  last 
mentioned  canal  it  went  only  a  short  distance  forward,  leaving  it 
through  the  opening  c.pal3  and  arriving  at  the  lower  surface  of  the 
primordial  neurocranium.  When  emerging  from  the  opening  c.pal3 
it  was  perhaps  accompanied  by  a  fine  branch  from  the  arteria  carotis 
interna  (Cf.  text  fig.  6). 

The  correctness  of  the  course  of  the  r.  palatinus  facialis  of  the 
fish  as  sketched  here  is  proved  by  the  conditions  in  recent  fishes,  in 
which  the  nerve  in  question  also  runs  in  a  similar  way  and  also  often 
more  or  less  closely  accompanies  the  a.  carotis  interna  for  a  correspond- 
ing distance.  (Allis  1897,  pp.  498,  685,  PI.  XXXVI,  fig.  61 ;  PI. 
XXXVII,  figs.  62,  63;  1901,  p.  182;  1909a,  pp.  43-55;  88,  185-186; 
1911a,  p.  290;  1919a;  1922a,  pp.  280-281;  1923,  p.  213;  Allen  1905, 
pp.  51-56;  Greil  1913,  PI.  LV,  fig.  2;  etc.;  cf.  also  Stensio  1923, 
pp.  1241-1248;  1925.) 

If  in  M.  raphcidolabis  there  was  an  anastomosis  between  the  r. 
palatinus    facialis   and   the   r.   palatinus   glossopharyngei,    this   anasto- 


126    Field  Museum  of  Natural  History — Geology,  Vol.  IV. 

mosis  must  have  been  situated  in  the  anterior  suborbital  part  of  the 
internal  carotid  canal  and  the  r.  palatinus  glossopharyngei  must  have 
arrived  there  through  the  canal  era,  the  sinus  si,  and  the  canal  c.cotn 
(Cf.  Allis  1897,  Pis.  XXXVI,  fig.  61;  PI.  XXXVII,  figs.  62,  63; 
1909a,  p.  186;  1911a,  p.  289-290).  The  canal  for  the  n.  ophthalmicus 
lateralis  has  already  been  dealt/  with,  and  I  call  attention  here  only 
to  the  fact  that  from  its  origin  in  the  lateral  wall  of  the  labyrinth 
region  it  goes  forward  and  upward  to  the  lateral  wall  of  the  orbito- 
temporal region, .  from  which  it  soon  arrives  up  and  into  the  dorsal 
wall,  continuing  into  this  through  the  entire  ethmoidal  region.  It  gives 
off  several  rami  in  dorsal  direction  to  the  sensory  canal  situated  dor- 
sally  of  it,  i.e.,  the  supraorbital  sensory  canal. 

After  having  dealt  with  the  trigeminus  and  facialis  nerves  and 
their  roots  and  ganglionic  complex,  we  can  now  understand  better  than 
before  the  relation  between  these  structures  and  the  jugular  vein,  and 
that  my  view  of  the  course  of  the  latter  ought  to  be  correct.  As  I 
suppose  this  vein  to  have  run,  it  must,  after  its  origin  in  the  orbit, 
have  passed  backward  below  the  r.  maxillaris  and  the  r.  mandibularis 
trigemini.  During  its  passage  through  the  basal  part  of  the  postorbital 
process  it  then  crossed  the  facialis  canal  on  the  dorsal  side,  thus  pass- 
ing ventrally  of  the  trigeminus  and  dorsally  of  the  facialis.  Although 
it  ran  rather  far  laterally  of  the  trigemino-facialis  ganglionic  complex 
and  did  not,  as  in  most  recent  forms,  traverse  this,  it  had,  however, 
obviously  retained  its  normal  relations  to  the  trigeminus  and  facialis 
nerves.     (Cf.  Allis  1922a,  pp.  260-264.) 

Neither  for  the  n.  trochlearis  nor  for  the  n.  abducens  have  canals 
so  far  been  found.  The  trochlearis  canal  was  probably  very  narrow, 
and  may,  therefore,  have  been  overlooked,  especially  as  the  medial 
wall  of  the  orbit  is  very  imperfectly  known  in  detail  at  the  place  where 
this  canal  ought  to  have  been  situated.  That  the  abducens  canal  is 
not  found  may  perhaps  be  explained  by  concluding  that  there  was  in 
reality  no  independent  canal  for  the  n.  abducens,  for  this  nerve  may 
perhaps  have  emerged  into  the  orbit  more  or  less  closely  associated 
with  the  r.  maxillaris  and  r.  mandibularis  trigemini,  as  it  does  in 
certain  recent  forms,  for  instance,  certain  Selachians.  (Allis  1901, 
p.  132;  etc.) 

A  rather  wide  canal  for  the  n.  oculomotorius  opens  into  the  orbit 
somewhat  in  front  of  the  canals  for  the  n.  ophthalmicus  profundus  and 
the  r.  ophthalmicus  superficialis  (V,  Figs.  8,  10,  11;  PI.  XXIII;  PI. 
XXV,  fig.  2;  PI.  XXVI,  figs.  1,  2).  A  short  distance  in  front  of  that 
canal,  the  wide  opticus  canal  (II,  Figs.  5,  10,  11 ;  PI.  XXIII ;  PI.  XXV, 


Macropetalichthyids  and  other  Arthrodires — StensiO     127 

fig.  2)  pierces  the  lateral  wall  in  an  anterolateral  direction,  opening 
into  the  anterior  half  of  the  orbit  not  far  above  the  floor.  In  its  most 
distal  (orbital)  part  it  receives  on  the  anterior  side  the  canal  for  the 
arteria  carotis  interna  (c.car.int),  which,  during  its  way  upwards  from 
the  ventral  wall,  makes  a  long  curve  forward,  so  that  for  a  short 
distance  it  even  traverses  a  posterior  part  of  the  ethmoidal  region. 

We  thus  find  that  the  arteria  carotis  externa  entered  the  distal 
part  of  the  opticus  canal.  From  there  it  evidently  must  have  traversed 
the  canal  in  medial  direction  to  reach  the  cavum  cerebrale.  But  just 
as  it  turned  medially  to  do  this  it  probably  gave  off  the  branch  known 
as  the  arteria  optica,  for  the  external  opening  of  the  opticus  canal 
has  on  its  anterior  side  distally  of  the  confluence  with  the  internal 
carotid  canal  a  distinct  emargination  (a.opt),  which  cannot  have  had 
any  other  function  than  to  transmit  a  vessel.  (Cf.  Allen  1905,  pp.  56- 
57;  Allis  1897,  p.  498;  1908a,  p.  258;  1908b,  p.  223;  1909a,  p.  186; 
1911a,  p.  290;  1911b,  p.  518;  1912a;  1912b,  pp.  489-490;  1912c,  p. 
586;  1914a;  1922a,  p.  168;  1923,  PI.  XIX;  Danforth  1912,  pp.  442- 
445  etc.)1 

The  way  in  which  the  arteria  carotis  interna  of  the  fish  entered  the 
cavum  cerebrale  may  perhaps  at  first  glance  appear  rather  strange,  as 
this  artery  in  fishes  generally  pierces  the  ventral  wall  of  the  primordial 
neurocranium  so  that  it  arrives  immediately  into  the  cavum  cerebrale 
and  not  first  into  the  opticus  canal.  But  a  closer  study  makes  it  clear 
that  the  difference  is  really  not  so  important,  for  in  certain  forms, 
e.g.,  Saurichthys  (Stensio  1925),  the  canal  for  the  internal  carotid 
opens  either  in  the  proximal  part  of  the  opticus  canal  or  at  the  tran- 
sition between  this  and  the  cavum  cerebrale  cranii.  We  have  there  a 
stage  intermediate  between  the  one  in  Macropetalichthys  raphcidolabis 
just  described  and  the  one  generally  occurring  in  fishes.  In  this  con- 
nection it  is  also  noteworthy  that  the  arteria  carotis  interna  in  Polyptcrus 
(Allis  1908b,  loc.cit;  1922a,  loc.cit;  Lehn  1918,  p.  380)  runs  exter- 
nally of  the  interorbital  wall  so  far  forward  that  it  enters  the  cavum 
cerebrale  either  together  with  or  close  behind  the  n.  opticus,  and  that 
in  Elasmobranchs  the  same  artery  within  the  lateral  wall  of  the  neuro- 
cranium goes  a  long  distance  forward  and  upward  in  direction  towards 
the  opticus  canal  before  entering  the  cavum  cerebrale.  (Allis  1912b, 
loc.cit;  1914a,  pp.  229-230,  236,  238,  etc.) 

'Another  interpretation  is  possible,  viz. : — that  the  arteria  pseudobranchialis 
efferens  reached  the  a.  carotis  interna  just  in  the  opticus  canal,  and  that  the 
a.  ophthalmica  magna  was  given  off  to  the  orbit  through  the  emargination  on 
the  anterior  side  of  the  opticus  canal.  This  emargination  would  consequently  in 
this  case  have  been  traversed  by  both  the  a.  ophthalmica  magna  and  the  a.  pseudo- 
branchialis efferens. 


128     Field  Museum  of  Natural  History — Geology,  Vol.  IV. 

Whether  a  canal  for  the  arteria  pseudobranchialis  efferens  was 
present  or  not  in  the  lateral  wall  could  not  be  decided  from  the  material 
available,  and  it  is  therefore  not  possible  to  conclude  anything  with 
certainty  concerning  the  relations  between  the  arteria  pseudobranchialis 
efferens  and  the  arteria  carotis  interna.  (Cf.  the  footnote  on  the  pre- 
ceding page.) 

As  is  seen  from  the  description  given  of  the  trigeminus  and  facialis 
canals,  there  is  no  real  trigemino-facialis  chamber  in  Macropetalichthys 
raphcidolabis. 

A  posterior  myodome  also  does  not  occur  in  M.  rapheidolabis,  and 
it  does  not  seem  probable  that  there  was  an  anterior  one  either.  A 
satisfactory  decision  in  the  latter  respect  is,  however,  not  as  yet  pos- 
sible, since  the  conditions  of  the  anterior  wall  of  the  orbit  are  very 
imperfectly  known. 

Since  the  postero-ventro-medial  corner  of  the  orbit  as  well  as  the 
postero- ventral  part  of  the  interorbital  wall  were  partly  covered  by 
matrix,  which  could  not  be  removed  without  hurting  the  fossil  as  a 
specimen,  the  pituitary  canal  (canal  for  the  pituitary  vein)  could  not 
be  observed,  but  I  do  not  doubt  that  it  actually  exists,  for  it  is,  as 
far  as  I  know,  without  exception  found  in  all  fishes,  although  in  those 
forms  which  have  a  posterior  myodome  it  is  a  part  of  this  and  has 
been  much  widened  and  transformed.     (Cf.  Allis  1909a,  pp.  183-208; 


cophih.lat 

C-ophth.Su.pV      *« 

cophthprqf 


o.ca-r.ext        cca.T-.ini 


Fig.  8.     Macropetalichthys  rapheidolabis 
Transverse   section   through   the   posterior   part  of   the  orbitotemporal   region 
and  the  antero-lateral  parts  (postorbital  processes)  of  the  labyrinth  region.    Layers 
of  substitution  bone  drawn  with  black  lines,  dermal  bones  with  vertical  striation. 
Cartilage  dotted.     X-K- 

Li,  L2,  Mi,  Pi,  dermal  bones  of  the  cranial  roof  (boundaries  approximately 
drawn);  c.car.cxt,  canal  for  the  arteria  carotis  externa;  c. car. hit,  canal  for  the 
arteria  carotis  interna;  c.ophth.lat,  canal  for  the  n.  ophthalmicus  lateralis;  c. 
ophth.prof,  canal  for  the  r.  ophthalmicus  profundus  trigemini;  c.ophth.sup.V , 
canal  for  the  r.  ophthalmicus  superficialis  trigemini ;  cv,  cavum  cerebrale  cranii ; 
ifc,  infraorbital  sensory  canal ;  jg,  canal  for  the  vena  jugularis  through  the 
postorbital  process  (somewhat  diagrammatically  drawn  as  it  really  would  not 
be  visible  to  this  extent  on  a  single  transverse  section)  ;  ju,  canal  in  the  part 
seen  in  the  section  for  the  vena  mandibulars,  behind  this  place  for  the  vena 
jugularis;  orb,  orbit;  soc,  supraorbital  sensory  canal;  III,  canal  for  the  n. 
oculomotorius ;  VII,  facialis  canal. 


Macropetalichthyids  and  other  Arthrodires — Stensio     129 

1911a,  p.  291;  1914a;  1918a;  1919a;  1922a,  p.  228;  1922b;  Gegenbaur 
1872,  pp.  75-79,  canalis  transversus  Allen  1905,  p.  81 ;  O'Donoghue 
1914,  pp.  440-441;  Stensio  1921,  pp.  62,  177-180;  1922,  p.  179; 
1923,  pp.  1244,  1262-1268;  1925,  Lehn  1918,  p.  380.) 

Owing  to  reasons  similar  to  those  which  prevented  study  of  the 
pituitary  canal,  it  was  not  possible  to  see  any  canal  for  the  vena  cere- 
bralis  anterior,  which  in  fishes  usually  perforates  the  upper  part  of 
the  interorbital  wall  and  goes  to  the  orbit.  (Cf.  Allis  1897,  PI.  21, 
figs.  9-1 1,  acvfr;  1903,  PI.  4,  fig.  9,  acvfr;  1909a,  p.  39;  1922a,  pp. 
261-262  Lehn  1918,  p.  380,  figs.  3,  4;  Stensio  1921,  pp.  168-169; 
1923,  pp.  1246-1247;  1925.) 

Ethmoidal  Region 

As  compared  with  the  labyrinth  and  orbito-temporal  regions  the 
ethmoidal  region  is  fairly  long,  its  breadth  being,  however,  also  con- 
siderable, and  even  so  considerable  that  it  exceeds  the  length.  On 
account  of  the  presence  of  the  extensive  orbital  bottom,  the  region  is 
not  marked  off  from  the  orbitotemporal  region  ventrally.  Higher  up 
above  the  bottom  of  the  orbit  it  is,  however,  much  broader  than  the 
latter  region,  forming  the  anterior  wall  of  the  orbits  and  projecting  on 
each  side  as  a  preorbital  process  in  the  normal  way  (Figs.  1,  3,  5;  Pis. 
XIX-XXI;  PI.  XXIV,  fig.  1;  PI.  XXV,  figs.  1,  2). 

Both  the  height  and  breadth  of  the  region  decrease  anteriorly,  the 
latter,  however,  proportionally  somewhat  more  than  the  former.  The 
anterior  end  is  imperfectly  preserved,  but  it  is  probable  that  it  was 
truncated,  and,  to  judge  from  the  conditions  in  Epipetalichthys  de- 
scribed below,  it  is  likely  that  it  was,  in  addition,  a  little  concave. 

Close  to  the  anterior  end  of  the  region  there  projects  from  the 
basal  parts  of  each  side  a  strong,  broad  process  (olf,  Figs.  1,  3,  5; 
Pis.  XXI-XXIII;  PI.  XXIV,  fig.  1)  in  a  lateral  and  somewhat  ven- 
tral direction.  This  process  has  its  distal  end  truncated  and  provided 
with  a  large  oval  opening  (na,  nf),  which,  as  is  evident  from  the  de- 
scription of  Epipetalichthys  below,  must  at  least  in  part  be  the  nasal 
opening.  Accordingly,  the  process  contains  the  nasal  cavity  and  rep- 
resents the  olfactory  capsule.  We  thus  have  here  an  olfactory  capsule 
that,  as  in  Elasmobranchs,  is  fairly  independent  and  projects  laterally 
in  relation  to  the  other  internasal  parts  of  the  ethmoidal  region.  (Cf. 
Allis  1923,  pp.  126-147.) 

A  closer  examination  of  the  nasal  opening  shows  that  this,  by  a 
process  of  bone  that  projected  forwards  from  the  posterior  wall,  is 
incompletely  subdivided  into  a  dorso-lateral  (na)  and  a  ventro-medial 


130    Field  Museum  of  Natural  History — Geology,  Vol.  IV. 

(»/)  portion.  Both  of  these  portions  are  directed  ventro-laterally,  but 
the  latter  considerably  more  so  than  the  former,  so  that  it  in  fact  is 
situated  on  the  ventral  side  of  the  nasal  capsule  (Figs,  i,  5; 
PI.  XXI ;  PI.  XXIII ;  PI.  XXIV,  fig.  1).  I  was  at  first  inclined  to  con- 
sider them  as  corresponding  to  the  two  nasal  apertures  generally  found 
in  fishes,  and  to  think  that  the  process  that  separates  them  would  be 
homologous  with  a  part  of  the  ala  nasalis  of  Elasmobranchs  (Allis 
1923,  pp.  126-147),  and  that  the  ala  nasalis  would  be  continuous  with, 
and  form  an  integral  part  of,  the  nasal  capsule.  But  after  having  read 
the  fine  memoir  on  Chlamydoselachus  recently  published  by  Allis 
(1923)  I  arrived  at  the  conclusion  that  what  has  been  called  above  the 
ventromedial  portion  («/)  of  the  nasal  opening,  really  represents  a  lat- 
eral part  of  the  nasal  fontanelle  of  Chlamydoselachus  and  certain  other 
Selachians  and  that,  accordingly,  the  other  portion  (na)  alone  is  the 
nasal  opening.  The  ala  nasalis  or  its  possible  homologue,  if  there  were 
one,  was  probably  entirely  without  ossification.  If  this  opinion  is  true, 
the  vein  commissure  that  in  Selachians  (Allis  1923,  pp.  126-147), 
Saurichthys  (Stensio  1925),  and  probably  in  most  fishes  (Allen  1905, 
PI.  1,  fig.  1;  PI.  Ill,  figs.  17,  18),  connects  the  orbito-nasal  vein  and 
the  anterior  facial  vein  with  each  other  must,  obviously,  have  traversed 
the  posterior  part  of  the  nasal  fontanelle.  Whether  this  fontanelle 
was  entirely  occupied  by  a  membrane  of  connective  tissue  or  whether 
it  was  more  or  less  occupied  by  cartilage  it  is  not  possible  to  decide. 

From  what  has  been  set  forth  regarding  the  nasal  capsule,  it  is 
clear  that  M.  rapheidolahis  in  this  regard  much  resembles  the  Elas- 
mobranchs. 

The  cavum  cerebrale  cranii  extends  only  a  short  distance  into  the 
posterior  part  of  the  region,  which,  therefore,  apart  from  certain 
canals,  in  the  whole  of  its  interior  consisted  of  cartilage.  On  account 
of  this  fact  we  cannot  conveniently  consider  it  to  be  composed  of  a 
number  of  walls,  as  in  the  case  of  the  other  regions,  but  will  have  to 
deal  with  it  as  a  solid  body  with  five  external  surfaces  which  are  well 
bounded  from  each  other.  These  surfaces  are  the  following :  a  ventral, 
a  posterior,  a  dorsal,  and  a  right  and  a  left  lateral. 

The  ventral  surface  is  broad  and  large  and  is  posteriorly  continuous 
with  the  ventral  surface  of  the  orbitotemporal  region  (Fig.  1 ; 
Pis.  XXI-XXIII).  Unfortunately  it  is  not  fully  preserved  in  its 
anterior  parts.  As  is  seen  from  the  figures  (the  transversal  section 
reproduced  in  Fig.  9  and  PI.  XXIV,  fig.  1)  it  is  slightly  concave 
both  in  transversal  and  rostro-caudal  direction.  And,  as  has  been 
pointed    out    above,    it    is    covered    by    the     external    bone    layer 


Macropetalichthyids  and  other  Arthrodires — Stensio     131 

throughout  its  extension.  Not  far  from  each  lateral  border  it  has  a 
distinct  sulcus  {s.pal,  Figs.  1,  9;  PI.  XXII),  which  leads  forward 
for  some  distance  from  the  opening  c.palz  (Fig.  1;  PI.  XXII). 
This  sulcus  was  evidently  developed  for  the  r.  palatinus  facialis,  and 
may,  perhaps,  in  addition,  also  have  lodged  a  small  arterial  branch 
given  off  from  the  arteria  carotis  interna  through  the  foramen  c.pal3. 
So  far  as  can  be  judged  there  is  no  indication  of  an  articulation  facet 
for  the  palatoquadrate  on  the  ventral  surface  of  the  region. 

Close,  medially,  to  each  groove  for  the  r.  palatinus  just  described, 
and  about  midway  between  the  anterior  end  of  the  region  and  the 
foramen  c.palz,  the  external  bone  layer  seems  to  show  faint  indications 
of  an  ossification  centre,  a  centre  which,  if  it  really  exists,  is  so  situ- 
ated that  the  bone  which  it  represents  corresponds  at  least  to  the 
exethmoid  (lateral  ethmoid)  of  fishes  in  general,  and  perhaps,  in  addi- 
tion, to  the  preethmoid  of  certain  fishes.  (Cf.  Allis  1897,  PI.  21,  figs. 
8-10,  SMX;  1898,  pp.  446-450;  1909a,  pp.  17-22;  Stensio  1921,  pp. 
61,  93-94;  I922,  PP-  184-186;  1923,  pp.  1247-1248;  1925,  etc.)  A 
positive  decision  in  this  respect  is,  however,  not  possible  until  more 
and  better  preserved  material  is  available  for  investigation. 

The  posterior  surface  of  the  region,  if  we  next  turn  to  this,  is, 
by  the  anterior  part  of  the  orbitotemporal  region  above  the  orbital 
floor,  subdivided  into  a  right  and  a  left  half,  each  forming  the  anterior 
surface  of  the  orbit  of  its  side.  As  it  could  not  be  cleaned  from 
matrix,  I  can  state  little  concerning  it.  It  may  have  had  a  foramen 
through  which  the  r.  ophthalmicus  superficialis  after  traversing  the 
orbit  entered  the  region,  but  nothing  can  be  said  about  the  posi- 
tion of  this  foramen.  As  has  already  been  pointed  out  above,  there 
probably  was  no  anterior  myodome  developed,  but  a  positive  de- 
cision in  regard  to  this  point  is  evidently  not  possible  until  material  is 
found  which- will  enable  us  to  undertake  a  detailed  examination  of  the 
posterior  parts  of  the  region.  The  olfactory  nerve  did  not  traverse 
the  orbit  and  accordingly  it  had  no  foramen  on  the  posterior  surface 
of  the  ethmoidal  region. 

The  dorsal  surface,  like  the  ventral  one,  is  large  and  broad  and 
posteriorly  continuous  with  the  dorsal  surface  of  the  orbitotemporal 
region  (Figs.  3,  5,  9;  Pis.  XIX-XX;  PI.  XXIV,  fig.  1;  PI.  XXV, 
figs.  1,  2;  PI.  XXVI,  figs.  1,  2).  It  is  slightly  convex,  both  in  trans- 
versal and  rostro-caudal  direction  (Fig.  9),  and  slopes  slightly  for- 
ward. In  its  most  anterior  parts  it  is  not  preserved  in  the  specimen 
examined,  being  either  crushed  together  with  the  dermal  cranial  roof 
or  destroyed  in  some  other  way.    From  the  closely  allied  Epipetalichthys 


132     Field  Museum  of  Natural  History — Geology,  Vol.  IV. 

to  be  described  below,  we  are,  however,  justified  in  concluding  that  the 
conditions  were  about  as  shown  in  Fig.  3,  i.e.,  that  there  probably 
was  a  deep,  broad,  antero-dorsally  directed  depression  (pfg)  at  the 
anterior  end  of  the  dorsal  surface,  and  that  this  depression  was  lined 
throughout  by  a  perichondral  bone  layer.  A  similar  depression  seems 
among  adult  fishes  to  occur  only  in  Elasmobranchs  (Cf.  Gegenbaur 
1872,  Pis.  IV-VIII,  etc.;  Allis  1913;  1923,  pp.  127-130;  Fritsch 
1895,  figs.  228,  230;  Woodward  1916-1919,  PI.  II,  fig.  1,  PI.  XXVI, 
fig.  3;  Daniel  191 5,  PI.  I,  fig.  1,  etc.),  and  we  would  accordingly  have 
here  a  very  remarkable  agreement  between  Epipetalichthys  and  Macro- 
petalichthys  on  the  one  hand,  and  the  Elasmobranchs  on  the  other.  As 
we  shall  see  from  the  account  given  below,  a  depression  of  the  same 
sort  probably  occurred  in  all  Arthrodires.  In  Elasmobranchs  the  de- 
pression, which  is  described  by  Allis  under  the  name  of  cavum  pre- 
cerebrale,  is  filled  by  a  fatty  tissue  and  this  was  probably  the  case 
also  in  the  Arthrodires,  since  the  dermal  bones  in  these  do  not  bend 
down  so  that  they  could  have  been  directly  superimposed  on  the  bottom 
of  the  depression,  but  are  situated  on  a  level  with  the  upper  borders 
of  this.  This  relatively  loose  position  of  the  dermal  skeleton  in  rela- 
tion to  the  primordial  neurocranium  at  the  anterior  end  of  the  ethmoidal 
region  explains  why  the  dermal  skeleton  is  generally  in  a  very  im- 
perfect state  of  preservation  there.  While  in  Elasmobranchs  the  cavum 
precerebrale  is  separated  from  the  cavum  cerebrale  in  most  cases  merely 
by  membranous  tissue,  there  was  here  in  Macropetalichthys  rapheido- 
labis  and  in  Epipetalichthys  certainly  a  thick  wall  of  cartilage  between 
them.  In  Lcemargus  borealis  I  have  also  found  that  the  wall  between 
the  cavum  precerebrale  and  the  cavum  cerebrale  is  to  a  large  extent 
formed  by  cartilage.    This  is  also  partly  shown  in  White  (1892,  PI.  I, 

%.  5)- 

From  the  dorsal  side  of  the  anterior  part  of  the  cavum  cerebrale 
cranii  a  rather  wide  canal  goes  dorsally  and  forward  to  the  upper  sur- 
face of  the  region,  where  it  opens  with  a  large  oval  foramen  (par, 
Fig.  3;  Pis.  XIX-XX;  PI.  XXVI,  fig.  1).  This  canal,  as  we  shall 
see,  lodged  the  pineal  or  parietal  organ  or  both  these  structures. 

Apart  from  this  canal,  several  fine  ones  for  vessels  and  nerve 
branches  naturally  opened  on  the  dorsal  surface  of  the  region.  In 
Pis.  XXI  and  XXIII  we  can  see  one  of  this  sort  (rm.ophth.lat),  that 
goes  from  the  canal  for  the  r.  ophthalmicus  lateralis  (c.ophth.lat)  a 
short  distance  upwards  and  forwards  to  the  anterior  part  of  the  supra- 
orbital sensory  canal  (soc).  This  sensory  canal  being,  like  the  others, 
situated  in  a  ridge  on  the  lower  side  of  the  dermal  bones,  there  must 


Macropetalichthyids  and  other  Arthrodires — Stensio     133 

evidently   have  been   a   paired   groove  corresponding  to   the   ridge,   a 
groove  running  as  is  shown  by  text  fig.  3. 

Finally,  the  lateral  surface  of  each  side  (Figs.  5,  9;  Pis.  XXI- 
XXIII;  PI.  XXIV,  fig.  1;  PI.  XXV,  figs.  1,  2)  is  strikingly  long, 
but  not  particularly  high.  It  faces  laterally  and  slightly  downwards 
and  is  somewhat  concave  in  dorso-ventral  direction.  From  its  antero- 
ventral  part  projects  the  large  nasal  capsule  (olf)  already  described, 
but,  as  is  seen  from  text  fig.  5  and  PI.  XXIV,  fig.  1,  this  does  not 
occupy  more  than  the  ventral  half  of  the  height  of  the  surface  at  this 
place.  As  far  as  can  be  seen,  there  is  no  articulation  facet  for  the 
palatoquadrate,  either  on  the  surface  itself  or  on  the  posterior  or  ventral 
parts  of  the  nasal  capsule.  This,  together  with  the  fact  pointed  out 
above  that  there  was  no  articulation  facet  on  the  ventral  surface  either, 
seems  to  indicate  that  the  palatoquadrate  actually  did  not  articulate 
against  the  region,  but  was  suspended  beneath  this  with  ligaments  in 
about  the  same  manner  as  in  the  Selachians. 


Ll =»„■-#* 


g±?^. 


a.pal 

Fig.  9.     Macropetalichthys  rapheidolabis 

Transverse  section  through  the  posterior  half  of  the  ethmoidal  region,  slightly 
anterior  to  the  anterior  end  of  the  cavum  cerebrale  cranii.  Layers  of  substitution 
bone  denoted  by  strong  black  lines ;  cartilage  dotted ;  dermal  bones  with  vertical 
striation.     XK- 

Li,  Mi,  dermal  bones  of  the  cranial  roof  (their  boundaries  not  fully  correct)  ; 
soc,  supraorbital  sensory  canal ;  s.pal,  groove  for  the  r.  palatinus  facialis  and 
perhaps  for  an  arterial  branch  too;  vx,  proximal  part  of  a  canal  running  up- 
wards in  the  cartilage,  probably  for  some  venous  vessel;  I,  canalis  tractus  ol- 
factorii. 

In  this  connection  it  may  also  be  pointed  out  that  the  postnasal 
part  of  each  lateral  surface  is  very  large,  a  condition  probably  caused 
by  the  insertion  of  a  powerfully  developed  part  of  the  musculus  con- 
strictor superficialis  (I)  homologous  to  the  muscle  of  the  Selachians  and 
Teleostomes  generally,  known  as  the  m.  levator  labii  superioris  (Vetter 
1874,  etc.),  levator  maxilla;  superioris  (Allis  1897,  pp.  552-556),  ab- 
ductor B  (Allis  1901,  PI.  II,  fig.  4;  PI.  12,  fig.  5)  or  preorbitalis 
(Luther  1909,  pp.  36-39).  If  this  were  not  the  case,  it  would  be 
very  difficult  to  find  a  satisfactory  explanation  for  the  considerable 
post-nasal  extension  of  the  lateral  surfaces. 


134    Field  Museum  of  Natural  History — Geology,  Vol.  IV. 

On  the  posterior  part  of  each  lateral  surface  there  are  found  the 
anterior  openings  of  two  fairly  wide  canals  (c.ophth.sup.V  ?  and  vy, 
Fig.  5 ;  PI.  XXII ;  PI.  XXIII ;  PI.  XXIV,  fig.  i )  which  evidently  issue 
from  the  orbit.  But  as  the  position  of  the  posterior  openings  of  these 
canals  and  their  course  within  the  preorbital  process  are  so  far  un- 
known, it  cannot  be  positively  decided  what  their  functions  were.  The 
dorsal  one  {c.ophth.sup.V?)  possibly  transmitted  the  r.  ophthalmicus 
superficialis  trigemini,  the  ventral  one  either  vessels  or  the  r.  maxillaris 
trigemini  and  the  n.  buccalis  lateralis  or  both  these  nerves  and  vessels. 

From  the  anterior  end  of  the  cavum  cerebrale  cranii,  a  paired, 
rather  low  but  wide  canal  (I,  Figs.  9,  10,  11,  12,  13;  Pis.  XXIII, 
XXVII)  issues  in  a  forward  and  somewhat  lateral  direction  to  the  nasal 
fossa  of  its  side,  being  during  the  entire  length  situated  very  low  in 
the  region.  This  canal,  which  narrows  anteriorly,  lodged,  as  far  as  I 
can  judge,  the  tractus  olfactorius  and,  at  the  most  anterior,  probably 
somewhat  widened  end,  the  lobus  olfactorius.  It  may,  therefore,  be 
called  the  canalis  tractus  olfactorii.  That  it  would  lodge  a  long  olfactory 
nerve  and  that  the  lobus  olfactorius  would  have  been  situated  at  the 
front  end  of  the  telencephalon  is  not,  as  will  be  set  forth  below,  in 
accordance  with  what  we  know  concerning  the  features  of  the  brain 
otherwise.  From  its  dorso-medial  side  there  are  given  oft"  in  the 
Field  Museum  specimen  two  canals  of  finer  calibre  which  run  antero- 
dorso-laterally  within  the  interior  of  the  region  {yx,  vx\,  PI.  XXVI, 
fig.  1),  and  which  probably  were  traversed  by  veins  draining  the  car- 
tilage and  dorsal  surface. 

Close  below  the  groove  for  each  supraorbital  sensory  canal,  we 
find  the  canal  for  the  r.  ophthalmicus  lateralis  (c.ophth.lat,  Fig.  9; 
Pis.  XXI,  XXIII),  from  which,  as  already  pointed  out,  branches 
(rm.ophth.lat)   run  upward  to  the  supraorbital  sensory  canal. 

Cavum  Cerebrale  Cranii  and  Brain 

Although  being  partly  much  narrower  than  the  primordial  neuro- 
cranium,  the  cavum  cerebrale  cranii  (cv,  Figs.  2,  4,  8,  10,  11 ;  Pis.  XX, 
XXI,  XXIII;  PI.  XXIV,  fig.  3;  PI.  XXV  figs.  1,  2;  PI.  XXVI,  figs. 
1,  2;  PI.  XXVII)  has  nevertheless  a  rather  considerable  size.  Ob- 
serving its  shape,  it  may  be  considered  to  consist  of  three  divisions, 
which  in  the  subsequent  description  are  called  the  posterior,  middle  and 
anterior   divisions   respectively. 

The  posterior  division  is  limited  entirely  to  the  posterior  narrow 
division  of  the  occipital  region,  and,  in  accordance  with  this,  it  is 
much  narrower  and  lower  than  the  other  two  {pd,  Figs.  10,  11;  PI. 


Macropetalichthyids  and  other  Arthrodires — Stensio     135 

XXVII).  Its  narrowest  part  is  situated  anteriorly,  just  at  the  tran- 
sition to  the  middle  division.  Behind  this  place  it  grows  slowly  and 
gradually. broader  and  a  little  lower  backwards,  but  whether  it  did  so 
quite  to  the  posterior  end  or  not  is  unknown.  Two  transverse  sections 
through  its  posterior  half  somewhat  anterior  to  the  cranio-spinal 
processes  are  seen  in  text  fig.  2. 

The  middle  division  (md,  Figs.  10,  11)  extends  through  the 
anterior  division  of  the  occipital  region,  the  whole  labyrinth  region  and 
a  short  posterior  part  of  the  orbitotemporal  region  (Cf.  also  Figs. 
2,  4,  8;  Pis.  XX,  XXIII;  PL  XXIV,  fig.  3;  PL  XXV,  figs.  1,  2;  PL 
XXVI,  figs.  1,  2),  and  is  the  largest  one  of  the  three  with  regard  to 
height  and  breadth,  but  its  length  is  about  equal  to  that  of  the  pos- 
terior division.  Its  maximum  height  is  situated  approximately  at  the 
transition  between  the  occipital  and  labyrinth  regions,  decreasing  from 
there  both  forward  and  backward,  although  only  very  slightly  for- 
ward. The  bulge  caused  by  the  vagus  and  the  other  nerves,  not  taking 
into  consideration  the  width,  attains  its  maximum  in  the  front  end  of 
the  division,  in  the  most  anterior  part  of  the  orbitotemporal  region, 
from  which  it  narrows  slightly  both  backward  and  forward. 

The  anterior  division  (ad,  Figs.  10,  11)  extends  through  the  an- 
terior larger  part  of  the  orbitotemporal  region  and  a  very  short 
posterior  part  of  the  ethmoidal  region,  where,  at  the  very  anterior  end, 
it  divides  into  a  right  and  a  left  half,  each  of  which  anteriorly  is  con- 
tinued by  the  canalis  tractus  olfactorii  (Figs.  10,  11;  PL  XXIII; 
PL  XXVI,  figs.  1,  2).  It  is  well  bounded  from  the  middle  division, 
being  both  lower  and  narrower  than  the  anterior  part  of  this.  The 
height  gradually  diminishes  forward  throughout  the  length  of  the  divi- 
sion, finally  becoming  equal  to  that  of  the  posterior  end  of  the  canalis 
tractus  olfactorii,  while  the  breadth,  on  the  contrary,  increases  slightly 
in  the  same  direction.  The  length  is  only  about  half  as  great  as  in 
the  other  two  divisions. 

The  floor  of  the  middle  division  is  slightly  convex,  that  of  the 
posterior  division  slightly  concave,  and  so  is  also  that  of  the  anterior 
division,  although  the  concavity  is  somewhat  larger  there  (Figs. 
10,  13;  PL  XXVI,  figs.  1,  2)  and  forms  a  shallow,  indistinct  fossa. 
In  the  median  parts,  this  fossa  has,  in  its  turn,  a  small,  very  slightly 
indicated  depression  (fhy,  Fig.  10),  which  is  so  situated  that  it 
must  have  lodged  at  least  the  most  ventral  part  of  the  hypophysis. 
The  lobi  inferiores  probably  had  their  position  laterally  of  this  de- 
pression, which  may  represent  the  last  remnant  of  an  originally  more 
pronounced  and  large  fossa  hypophyseos. 


136    Field  Museum  of  Natural  History — Geology,  Vol.  IV. 


,.JII  ..c.opkth.SupV 

VII 


Fig.  10.    Macropetalichthys  rapheidolabis 

Shape  of  the  cavum  cerebrale  cranii  in  ventral  view.  With  the  exception 
of  the  posterior  division,  which  is  restored  from  specimens  in  the  American 
Museum,  entirely  after  the  Field  Museum  specimen.     X24. 

ad,  anterior  division  of  the  cavum  cerebrale  cranii;  afr,  acustico-facialis 
recess ;  a.opt,  division  of  the  external  opening  of  the  opticus  canal,  probably  for 
the  arteria  optica;  c.bucc.lat,  canal  for  the  lateralis  fibres,  representing  the  n. 
buccalis  lateralis  and  possibly  also  for  certain  general  cutaneous  fibres  to  the 
n.  facialis ;  c.car.int,  canal  for  the  arteria  carotis  interna ;  c.ophth.lat,  canal  for 
the  n.  ophthalmicus  lateralis ;  c.ophth.prof,  canal  for  the  r.  ophthalmicus  pro- 
fundus; c.ophth.sup.V ,  canal  for  the  r.  ophthalmicus  superficialis  trigemini;  c.pah, 
canal  for  the  r.  palatinus  facialis  from  the  facialis  canal  to  the  orbit;  dx,  canal 
for  a  dorsal  branch  from  the  n.  linese  lateralis ;  fhy,  depression  probably  for  the 


Macropetalichthyids  and  other  Arthrodires — Stensio     137 

hypophysis;  md,  middle  division  of  the  cavum  cerebrale;  n.l,  canal  for  the 
n.  lineae  lateralis ;  pd,  posterior  division  of  the  cavum  cerebrale  cranii ;  v.lb,  canal 
leading  from  the  labyrinth  cavity  to  the  vagus  canal,  probably  for  a  large  vein; 
I,  canalis  tractus  olfactorii ;  II,  division  of  the  opticus  canal  for  the  n.  opticus ; 
III,  canal  for  the  n.  trochlearis;  V,  proximal  wide  part  of  the  trigeminus  canal, 
forming  a  trigeminus  recess ;  V»,»,  distal  narrow  part  of  the  trigeminus  canal 
traversed  by  the  r.  maxillaris,  r.  mandibularis  trigemini  and  the  n.  buccalis 
lateralis ;  VII,  facialis  canal ;  VIII,  acusticus  canal ;  IX,  glossopharyngeus  canal ; 
Xm,  vagus  canal  transmitting  the  n.  vagus  and  the  v.  cerebralis  posterior. 

In  the  posterior  part  of  the  roof  of  the  anterior  division,  there  is, 
in  the  Field  Museum  specimen,  a  median,  unpaired  diverticle  (ep) 
situated  as  shown  by  Fig.  11,  i.e.,  it  extends  a  short  distance 
upward  into  the  dorsal  wall  of  the  orbitotemporal  region.  Somewhat 
in  front  of  this  diverticle,  the  canal  par  to  which  reference  has  already 
been  made  issues  from  the  same  division  in  an  antero-dorsal 
direction  to  the  dorsal  surface  of  the  posterior  part  of  the  ethmoidal 
region,  opening  there  with  a  rather  large,  oval  foramen  (par,  Figs. 
3,  11-13;  Pis.  XIX,  XX;  PI.  XXVI,  fig.  1). 

According  to  the  observations  recently  made  by  Woodward  (1922, 
p.  31,  fig.  3)  the  pit  that  regularly  occurs  on  the  lower  side  of  the 
pineal  plate  in  non-Macropetalichthyid  Arthrodires  is  paired  in  Tita- 
nichthys,  a  fact  which  causes  Woodward  to  consider  that  the  epiphysis 
there  was  a  paired,  symmetrically  situated  organ.  We  are  thus  in 
Titanichthys  concerned  with  a  form  in  which  the  parietal  and  pineal 
organs  probably  were  situated  beside  one  another  (Cf.  Goodrich  1909, 
p.  25 ;  Plate  1923,  pp.  743-753)  and  it  seems  to  be  a  matter  of  course 
that  in  all  typical  non-Macropetalichthyid  Arthrodires,  as,  for  instance, 
Dinichthys  and  Coccosteus,  they  must  have  been  situated  exactly  as 
in  Titanichthys. 

In  Macropetalichthys  rapheidolabis  the  bone-plate  Mx  (text  fig.  15) 
of  the  dermal  cranial  roof  with  its  posterior  part  evidently  corresponds 
to  the  pineal  plate  (Pi,  Fig.  14)  of  Titanichthys  and  other  typical 
non-Macropetalichthyid  Arthrodires.  The  canal  by  which  it  is 
said  by  Eastman  (1908a,  p.  104;  1908b,  p.  169)  to  be  perforated 
seems  to  have  such  a  position  that  it  must  form  the  distal  continua- 
tion of  the  canal  par,  and  at  least  ventrally  correspond  to  the  pit  on 
the  lower  side  of  the  pineal  plate  in  the  non-Macropetalichthyid  Arthro- 
dires. These  facts,  together  with  the  circumstance  that  Macropetalich- 
thys rapheidolabis  in  most  other  respects  is  fairly  closely  allied  to  the 
other  Arthrodires,  make  it  highly  probable  that  the  parietal  and  pineal 
organs  in  it  were  situated  as  in  these.  If,  therefore,  these  organs  in 
the  other  Arthrodires  occupied  a  position  beside  one  another,  they 
would  obviously  in  M.  rapheidolabis  both  have  been  situated  in  the 
canal  par,  and  the  diverticle  ep  would  thus  have  lodged  no  part  of  the 


138    Field  Museum  of  Natural  History — Geology,  Vol.  IV. 

brain  and  might  in  such  a  case  very  well  be  thought  to  be  occasionally 
developed  in  the  Field  Museum  specimen.  That  the  diverticle  ep  can- 
not probably  have  lodged  the  pineal  organ  is  also,  as  kindly  pointed 
out  to  me  by  Professor  N.  Holmgren  of  Stockholm,  indicated  by  its 
position  very  far  back. 

Leaving  this  question,  we  turn  to  the  canals  that  issue  from  the 
three  divisions  of  the  cavum  cerebrale  cranii,  beginning  posteriorly  and 
proceeding  forward. 

It  would  be  expected  that  several  canals  for  spino-occipital  nerves 
had  left  the  posterior  division  of  the  cavum  cerebrale  cranii,  but, 
as  pointed  out  above,  no  such  canals  could  be  observed  in  the 
material  so  far  investigated,  a  fact  which  of  course  does  not  neces- 
sarily imply  that  they  are  lacking,  for  the  possibility  is  to  be  taken 
into  consideration  that  they  are  very  minute  and  on  that  account  can 
only  exceptionally  be  distinctly  seen,  and  then  only  in  especially  well- 
preserved  specimens. 

From  the  middle  division  of  the  cavum  cerebrale  issues  most  pos- 
teriorly the  wide  vagus  canal  (Xvn  Figs.  10,  11,  PI.  XX;  PI.  XXIII; 
PI.  XXV,  figs.  1,  2;  PI.  XXVI,  figs.  1,  2).  Some  distance  anterior  of 
this  appears  the  glossopharyngeus  canal  (IX)  and  most  anteriorly, 
rather  close  to  each  other,  the  acusticus  canal  (VIII),  the  facialis  canal 
(VII)  and  the  trigeminus  canal-  (V).  The  acusticus  and  facialis  canals 
take  their  origin  from  a  common  recess  on  the  side  of  the  division,  a 
recess  which  I  have  termed  the  acustico-facialis  recess  (afr).  All  the 
canals  enumerated  leave  the  basal  parts  of  the  division.  Besides  these 
there  are,  however,  three  other  canals  situated  higher  up,  all  of  which 
must  have  been  traversed  by  vessels.  The  most  posterior  one  of  these, 
(v.lb,  Fig.  11;  PI.  XX;  PI.  XXV,  figs.  1,  2;  PI.  XXVI,  figs.  1,  2), 
which  is  very  wide  and  goes  from  the  postero-dorso-medial  parts  of 
the  labyrinth  cavity  to  the  dorsal  part  of  the  vagus  canal  at  the  tran- 
sition between  this  canal  and  the  division  in  question  of  the  cavum 
cerebrale,  probably  transmitted  a  vein  that  drained  the  labyrinth.  The 
two  remaining  canals  (vlt  v2,  Fig.  11;  PI.  XX;  PI.  XXV,  figs. 
1,  2;  PI.  XXVI,  figs.  1,  2,  3)  are  both  narrow,  connect  the  dorsal  parts 
of  the  division  above  the  acustico-facialis  recess  with  the  labyrinth 
cavity  and  most  probably  may  have  been  traversed  by  arteries. 

From  the  anterior  division  of  the  cavum  cerebrale  cranii,  the  oculo- 
motorius  canal  (III,  Fig.  11;  PI.  XXIII;  PI.  XXV,  figs.  1,  2;  PI. 
XXVI,  figs.  1,  2),  the  opticus  canal  (II)  and  the  canal  for  the  tractus 
olfactorius  (I)  take  their  origin,  the  one  last  mentioned  from  the  an- 
terior end  and  the  one  first  mentioned  far  posteriorly,  not  so  very  far 


Macropetalichthyids  and  other  Arthrodires — Stensio     139 


from  the  middle  division.  Besides  these  canals  there  issue  from  the 
anterior  division,  as  we  have  already  seen,  the  canal  par  and  the  diver- 
ticle  ep. 

Guided  by  the  detailed  knowledge  we  possess  of  the  canals  for  the 
cranial  nerves,  we  are  to  a  certain  extent  able  to  draw  conclusions  con- 
cerning the  brain  and  its  position  in  the  cavum  cerebrale.  From  the 
place  of  exit  and  direction  of  the  acusticus  facialis  and  trigeminus 
canals,  it  is  obvious  that  the  roots  of  the  n.  acusticus,  n.  facialis  and 
n.  trigeminus  must  have  left  the  medulla  oblongata  in  the  anterior  half 
of  the  middle  division  of  the  cavum  cerebrale  and,  accordingly,  that 
the  medulla  oblongata  reached  far  forward  in  the  middle  division  (myl. 
Figs.  12,  13).  The  most  anterior  part  of  this  division  was,  how- 
ever, certainly  occupied  by  the  whole,  or,  at  least,  the  larger  posterior 
portion  of  the  mesencephalon  (tnes,  Figs.  12,  13).  Dorsally  of  the 
mesencephalon  and  the  anterior  portion  of  the  medulla,  there  probably 


c.ophth.Jat  par 


c.ophih.sup.V 
op   \ 


Fig.  11.    Macropetalichthys  rapheidolabis 

Shape  of  the  cavuum  cerebrale  cranii  in  lateral  view.  After  the  Field  Museum 
specimen,  with  the  exception  of  the  posterior  division,  which  is  restored  after  a 
specimen  in  the  American  Museum.     X^- 

ep,  canal  of  doubtful  importance,  probably  an  occasional  structure ;  par,  pineal 
canal,  probably  for  both  the  parietal  and  pineal  organs  (at  least  in  the  basal  half)  ; 
'1.  v»,  canals  probably  for  arteries  from  the  cavum  cerebrale  cranii  to  the 
labyrinth  cavity ;  vx,  vx,,  canals  probably  for  veins.  Other  letters  of  reference 
as  in  text  fig.  10. 

existed  a  rather  well-developed  cerebellum  (met,  Figs.  12,  13)  and 
the  anterior  half  of  the  middle  division  may  accordingly  have  been 
rather  well  filled,  while  the  posterior  half  of  the  same  division,  which 
lodged  only  the  posterior  longer  portion  of  the  medulla  oblongata, 
cannot  have  been  filled  by  this.  The  conditions  there  must  have  been 
about  as  seen  in  Figs.  12,  13.  The  medulla  was  undoubtedly  long, 
but  it  is  impossible  to  say  with  certainty  how  far  back  it  extended. 

The  anterior  division  of  the  cavum  cerebrale  must,  as  is  easily 
understood,  have  lodged  the  telencephalon  and  diencephalon  (Figs. 
12,  13),  and  in  addition  probably  a  short  anterior  portion  of  the  mesen- 


140    Field  Museum  of  Natural  History — Geology,  Vol.  IV. 

cephalon.  The  diencephalon  (die)  seems  to  have  been  long,  probably 
reaching  forward  to  about  the  middle  of  the  division,  but,  may  as  far  as 
can  be  judged,  not  have  been  so  high  as  this.  The  hypophysis,  and,  if 
they  were  developed,  the  saccus  vasculosus  and  the  lobi  inferiores  as 
well,  may  have  been  situated  in  the  shallow  concavity  in  the  floor  of 
the  anterior  division  approximately  in  the  way  shown  in  text  fig.  13. 
The  hypophysis  occupied,  however,  a  small  depression  of  its  own  in  the 
middle  part  of  the  concavity  (fhy,  Fig.  10).  The  canal  par,  prob- 
ably lodged  both  the  parietal  and  pineal  organs,  while  the  importance 
of  the  diverticle  ep  is  still  doubtful. 

The  telencephalon  (tel,  Figs.  12,  13)  probably  occupied  about 
the  anterior  half  of  the  anterior  division  of  the  cavum  cerebrale.  It 
must  have  been  comparatively  broad  and  low  and  anteriorly  it  was 
probably  bilobated,  a  portion  of  it  on  each  side  extending  into  the 
proximal  part  of  the  canalis  tractus  olfactorii  of  its  side.  From  each 
of  the  two  anterior  lobes  the  tractus  olfactorius  (I)  went  through  its 
long  canal  anteriorly  and  laterally  to  the  lobus  olfactorius  (l.olf), 
which,  as  far  as  can  be  judged,  was  situated  close  to  the  nasal  pit. 

From  what  has  now  been  said  it  will  be  evident  that  the  cavum 
cerebrale  cranii  only  to  a  certain  extent  reflects  the  shape  of  the  brain. 
But  despite  this  it  seems  to  be  rather  clear  that  the  brain  cannot  have 
resembled  that  in  Dipnoi,  Crossopterygii  or  Actinopterygii,  but  that  it 
may  have  been  Elasmobranchian-like.  At  least  with  regard  to  certain 
anterior  parts  it  probably  was  much  as  in  Hcptanchus  (Cf.  Gegenbaur 
1898,  Fig.  455)  and  Chalmydoselachus  (Allis  1923,  PI.  22,  fig.  59). 

The  restoration  of  the  brain  given  in  text  figs.  12  and  13  is  based 
chiefly  on  the  conditions  in  Heptanchus  and  is  of  course  to  a  large  extent 
rather  arbitrary. 

DERMAL  BONES  OF  THE  PRIMORDIAL  NEUROCRANIUM 

The  ventral  side  of  the  primordial  neurocranium  was  entirely  with- 
out dermal  bones,  the  parasphenoid  of  Cope's  (1891,  p.  453,  PI.  29, 
fig.  2;  PI.  30,  fig.  1)  and  Eastman's  (1908a,  pp.  108-109;  1908b,  pp. 
174-175)  descriptions  being  simply  the  external  bone  layer  on  the 
ventral  side  of  the  primordial  neurocranium. 

The  dorsal  side  of  the  primordial  neurocranium,  on  "the  contrary, 
is,  as  known,  completely  covered  by  a  cuirass  of  dermal  bones,  a  cuirass, 
which,  in  this  paper,  is  generally  referred  to  as  the  dermal  cranial  roof. 
On  account  of  the  postero-medial  displacement  of  the  eyes,  the  orbital 
openings  have  become  entirely  encircled  by  the  dermal  cranial  roof. 


Macropetalichthyids  and  other  Arthrodires — Stensio     141 


Fig  12.    Macropetalichthys  rapheidolabis 

Hypothetical  shape  of  brain  from  above  in  relation  to  the  cavum  cerebrale 
cranii.  Brain  with  a  dark  tone,  outlines  of  the  cavum  cerebrale  indicated  by  a 
continuous  line.     X?4- 

die,  diencephalon ;  l.olf,  lobus  olfactorius;  mes,  mesencephalon;  met,  cerebel- 
lum ;  myl,  medulla  oblongata ;  nac,  nasal  pit ;  par,  parietal  or  pineal  organs  or 
both;  tel,  telencephalon;  I,  tractus  olfactorius;  II,  n.  opticus;  III,  n.  oculo- 
motorius;  V,  roots  of  the  trigeminus  proper;  VII,  facialis  roots  +  lateralis 
roots  of  the  entire  trigemino-facialis  complex;  VIII,  root  of  the  n.  acusticus ; 
IX,  root  of  the  n.  glossopharyngeus ;  X,  roots  of  the  n.  vagus  and  the  n.  lineae 
lateralis. 


142     Field  Museum  of  Natural  History — Geology,  Vol.  IV. 

The  general  shape  of  the  dermal  cranial  roof  may  be  seen  in 
Fig.  15.  The  restoration  given  of  it  by  Dean  (1901,  Fig.  12,  p.  116) 
is  almost  correct,  while  the  one  published  six  years  later  by  Eastman 
is  wrong  with  regard  to  its  general  proportions  (Eastman  1908a, 
Fig.  19),  as  becomes  evident  by  comparing  Eastman's  restoration  with 
the  specimen  he  figured  in  PI.  rrof  his  description. 

Concerning  the  number  of  bones  composing  the  dermal  cranial  roof, 
1  have  nothing  new  to  add  here  to  what  is  known  from  earlier  descrip- 
tions. The  boundaries  between  the  various  bones,  on  the  other  hand, 
I  have  in  certain  places  found  to  be  somewhat  different  from  those 
shown  in  Dean's  (1901)  and  Eastman's  (1908a)  restorations.  But 
my  own  restoration  (Fig.  15)  does  not  claim  to  be  fully  accurate 
in  this  respect,  as  the  material  investigated  by  me  was  both  very 
limited  and  imperfectly  preserved  with  regard  to  the  dermal  cranial 
roof. 


Fig.  13.    Macropetalichthys  rapheidolabis 

Hypothetical  shape  of  brain  from  the  left  side  in  relation  to  the  shape  of  the 
cavum  cerebrale  cranii.  Brain  with  a  dark  tone,  outlines  of  the  cavum  cerebrale 
indicated  by  a  continuous  line.     X24- 

hyp)  hypophysis  and  other  ventral  parts  of  the  diencephalon.  Other  letters 
of  reference  as  in  text  fig.  12. 

As  in  a  paper  which  I  expect  to  publish  later,  I  think  I  can  show 
that  the  dermal  bones  of  the  cranial  roof  in  Arthrodires  have  evolved 
independently  of  those  in  the  Telcostomi,  or,  to  put  it  differently,  that 
they  are  not  directly  comparable  to  those  in  the  Teleostomi,  I  have  let- 
tered them  here  in  text  fig.  15  with  indifferent  letters. 

Each  plate  5"  has,  posteriorly,  close  to  the  posterior  border,  a  ver- 
tically descending  lamina  which  is  rigidly  fixed  to  the  cranio-spinal 
process  of  its  side.  In  the  specimens  investigated  by  me,  this  lamina 
is  unfortunately  very  imperfectly  preserved,  so  that  its  extension  and 
relations  could  not  be  established  with  certainty.  In  M.  pelmensis  it 
is,  however,  well-preserved,  and  it  seems  there  to  cover  the  posterior 
surface  of  the  cranio-spinal  process  and  to  be  very  large  and  meet  its 
fellow  of  the  opposite  side  in  the  median  line. 


Macropetalichthyids  and  other  Arthrodires — Stensio     143 

Hennig  in  his  description  of  M.  pehncnsis,  did  not  perceive  the 
true  nature  of  this  lamella,  but  considered  it  to  be  a  paired  lateral 
occipital  (Hennig  1907,  pp.  585-586,  Fig.  3,  OL)1.  This  ventral  lamella 
is  necessary  for  the  support  of  the  much  lengthened,  posterior  parts  of 
the  dermal  cranial  roof.  A  parallel  to  this  is  found  in  sturgeons 
(both  Polyodontids  and  Acipenserids)  in  which  a  lamella  issues  from 
each  extrascapular  bone  downwards  in  such  a  way  that  it  covers  and 
is  fixed  to  the  anterior  surface  of  the  cranio-spinal  process  of  its  side. 
Accordingly,  it  is  not  homologous  with  that  in  Macro petalichthys. 
In  Saurichthys,  in  which  also  a  strong  cranio-spinal  process,  very  sim- 
ilar to  that  in  sturgeons,  occurs,  a  descending  lamina  from  the  dermal 
cranial  roof  is,  on  the  contrary,  entirely  lacking  (Stensio  1925). 

The  plate  M  is  said  by  Eastman  (1908a,  p.  104;  1908b,  p.  169) 
to  be  pierced  by  a  fine  canal  just  above  the  canal  par  in  the  roof  of  the 
primordial  neurocranium.  The  material  investigated  by  me  was  not 
satisfactorily  preserved  at  this  place,  and  I  have  therefore  not  been 
able  to  verify  the  correctness  of  Eastman's  statement  as  to  this  point. 


Fig.    14.      TlTANICHTHYS   AGASSIZI,    NEWB. 

Dermal  cranial  roof  and  infraorbital  plate.  After  Eastman  (1008a.  fig.  29). 
Sensory  canal  grooves  omitted.  Much  diminished.  Pi,  pineal  plate;  R,  rostral 
plate;  orb,  orbital  opening. 

DERMAL  BONES  OF  THE  CHEEK 
No  remains  of  dermal  bones  were  found  which,  with  certainty,  be- 
longed to  the  cheek,  and  it  is  rather  probable  that  these  bones  were 
either  much  reduced  or  entirely  lacking  in  the  fish.  That  the  plate  Plf 
situated  latero-ventrally  of  the  orbital  opening,  is  no  infraorbital  bone, 
is  evident  both  from  the  fact  that  the  eye  has  shifted  a  rather  consider- 
able distance  postero-medially  and  from  the  course  of  the  sensory  canals, 
as  we  shall  understand  from  the  account  of  these  given  below. 

'The  description  which  Hennig  (1007)  gives  of  M.  pelmensis  is  also  in  most 
other  respects  very  incorrect,  the  anatomical  features  of  the  fish  having  been 
for  the  most  part  entirely  misunderstood. 


144     Field  Museum  of  Natural  History — Geology,  Vol.  IV. 

VISCERAL   SKELETON 

Remains  of  the  visceral  skeleton  have  hitherto  not  been  found. 
Despite  this  we  are,  however,  able  to  draw  certain  conclusions  about  it. 

The  palatoquadrate  was  not  coalesced  with  the  primordial  neuro- 
cranium,  but  was  an  independent  element.  As  far  as  we  can  judge, 
it  did  not  articulate  with  the  primordial  neurocranium,  either  anteriorly 
or  posteriorly,  and,  if  this  be  true,  it  must  have  been  suspended  merely 
by  ligaments  below  the  ethmoidal  region  and  by  means  of  the  hyoid  arch 
below  the  labyrinth  region.  Accordingly,  its  relations  to  the  primordial 
neurocranium  seem  to  have  been  about  as  in  sturgeons  and  recent  sharks 
(except  the  Notidanide,  in  which,  as  known,  there  exists  a  postorbital 
articulation  between  the  palatoquadrate  and  primordial  neurocranium). 


cpp 


Fig.  15.    Macropetalichthys  rapheidolabis 

Restoration  of  the  dermal  cranial  roof.  Course  of  the  sutures  probably  in 
places  not  fully  correct.  Sensory  canals  marked  with  double  dotted  lines  and 
colors.     Ornament  of  the  bones  omitted.     XM- 

Li,  L2,  Ls,  Mi,  M2,  Pi,  P2,  S,  dermal  bones  of  the  cranial  roof ;  c.pp,  sensory 
canal  commissure,  probably  corresponding  to  the  posterior  head  lines  of  pit  origin 
in  recent  fishes  (red)  ;  ifc,  infraorbital  sensory  canal  (blue)  ;  Ic,  cephalic  divi- 
sion of  the  lateral  line(  red)  ;  olf,  nasal  capsule;  orb,  orbital  opening;  poc,  pre- 
opercular  sensory  canal   (yellow)  ;  soc,  supraorbital  sensory  canal  (green). 


Macropetalichthyids  and  other  Arthrodires — Stensio     145 

Probably  there  was  in  relation  to  the  palatoquadrate,  a  large  musculus 
preorbitalis  (Cf.  the  description  of  the  ethmoidal  region  above). 

If  my  interpretation  of  the  canal  c.hy  as  the  canal  for  the  vena 
hyoidea  is  correct,  it  is  obvious  that  the  hyoid  arch  articulated  against 
the  primordial  neurocranium  closely  anterior  to  the  external  opening 
of  this  canal,  or,  at  least  that  the  hyoid  arch,  if  it  did  not  articulate 
against  the  primordial  neurocranium,  had  its  dorsal  end  situated  closely 
anterior  to  this  place,  for  it  must  of  course  have  been  situated  an- 
terior to  the  hyoid  vein.  Or  to  express  it  in  another  way,  the  hyoid 
vein  must  have  passed  upward  to  the  jugular  vein  along  the  pos- 
terior side  of  the  hyoid  arch.  Whether  the  dorsal  end  of  the  hyoid 
arch  was  situated  ventrally  of  the  vena  jugularis,  as  in  Selachians,  or 
dorsally  of  the  same  vein  as  in  the  Teleostomi,  it  is  impossible  to  decide 
from  the  specimens  investigated  (Cf.  Allis  1915,  1918b). 

Of  much  interest  in  this  connection  is  the  fact  that  the  jugular 
vein  as  well  at  the  upper  end  of,  as  anterior  and  posterior  to  the  hyoid 
arch,  went  within  the  lateral  wall  of  the  primordial  neurocranium  and 
that,  accordingly,  a  shifting  of  the  place  of  articulation  of  the  dorsal 
end  of  the  hyoid  arch  against  the  primordial  neurocranium  could  take 
place  in  a  dorsal  or  ventral  direction  without  affecting  the  jugular  vein. 
As  the  jugular  vein  in  Eusthenopteron1  also  passed  within  the  lateral 
wall  of  the  primordial  neurocranium  to  about  the  same  extent  as  in 
Macropetalichthys  and  probably  did  also  in  other  Crossopterygians 
(Cf.  Stensio  1922,  p.  201,  the  long  intramural  course  of  the  truncus 
hyoidemandibularis  facialis)  one  suspects  that  this  was  originally  the 
case  in  all  fishes. 

If  this  suspicion  be  true,  the  mainly  extramural  course  of  the  jugu- 
lar vein  in  most  fishes  would  be  due  to  reduction  of  certain  lateral 
parts  of  the  lateral  walls  of  the  primordial  neurocranium.  And,  more- 
over, it  would  be  very  easy  to  understand  how  the  place  of  articulation 
of  the  hyoid  arch  could  have  shifted  upwards  to  the  dorsal  side  of 
the  jugular  vein  in  the  Teleostomi.  Finally,  the  hyomandibular  of  the 
Teleostomi,  would  not,  as  Allis  (1915,  1918b)  supposes,  have  incorpo- 
rated at  its  dorsal  end  certain  parts  lacking  as  such  in  the  hyomandib- 
ular of  the  Elasmobranchs.  The  conditions  found  in  Macropetalich- 
thys and  Eusthenopteron  with  regard  to  the  vena  jugularis  and  the  vena 
hyoidea  thus  seem  to  make  certain  of  the  views  recently  advanced  by 
Allis  (1915,  1918b)  concerning  the  homologies  of  the  hyomandibular 
of  fishes  very  doubtful. 

'Observation  made  on  a  well  preserved  specimen  in  the  collection  of  the 
Palseontological  Institution  of  Upsala. 


146    Field  Museum  of  Natural  History — Geology,  Vol.  IV. 

The  first  branchial  arch  followed  not  very  far  behind  the  hyoid 
arch.  On  account  of  the  cranio-vertebral  articulation  found  in  most 
or  all  Arthrodires,  there  is  no  reason  to  believe  that  the  branchial  basket 
extended  backwards  into  the  abdominal  region  of  the  trunk,  but  was 
limited  to  the  suboccipital  part  q£  the  head. 

DENTITION 
Unfortunately  the  dentition  is  so  far  entirely  unknown. 

SENSORY  CANALS  OF  THE  HEAD 
The  sensory  canals  are  found  preserved  on  the  head  only  in  the 
dermal  cranial  roof.  They  consist  there  of  tubes  which  are  situated 
within  the  bones,  or,  more  exactly,  in  ridge-like  thickenings  on  the 
lower  side  of  the  bones  (Figs.  4,  8,  9).  Accordingly  they  have  a 
very  deep  position  (Cf.  Kaer  1915,  p.  12),  a  fact  which  explains  that 
there  are  frequently  traces  of  them  preserved  even  in  specimens  in 
which  the  dermal  bones  have  almost  entirely  weathered  away,  as,  for 
instance,  in  the  specimen  reproduced  in  Pis.  XIX,  XX.  At  least  in 
the  larger  parts  of  their  extension  they  open  outwards  with  a  double 
series  of  fine  tubuli.  These  tubuli  occur  in  great  number  and  are 
situated  fairly  close  to  each  other,  conditions  which  seem  to  indicate 
that  they  were  much  more  numerous  than  the  sensory  canal  organs. 
In  any  case  they  are  much  more  numerous  than  the  nerve-canals  lead- 
ing to  the  sensory  canals.  , 

On  account  of  the  fortunate  circumstance  that  the  fine  canals  for 
the  nerve  branches  to  the  sensory  canal  organs  are  lined  by  a  thin 
layer  of  bone,  they  could  be  preserved,  and  thus  enable  us  to  get  a 
rather  complete  knowledge  of  the  manner  in  which  the  sensory  canals 
were  innervated.  With  the  help  of  this  knowledge  it  is  not  difficult 
to  homologize  the  sensory  canals  in  Macropetalichthys  rapheidolabis 
with  those  in  recent  fishes,  as  will  be  evident  from  the  subsequent  ac- 
count. With  regard  to  the  terminology,  I  shall  follow  Allis  (1889; 
1900;  1901 ;  1903;  1905;  1923)  with  the  exception  only  that  in  accord- 
ance with  Ewart  (1892),  Ewart  and  Cole  (1895),  Ewart  and 
Mitchell  (1892),  and  Cole  (1896a,  b;  1898)  I  limit  the  infraorbital 
sensory  canal  to  those  parts  innervated  by  the  n.  buccalis  lateralis  and 
n.  oticus  lateralis. 

The  supraorbital  sensory  canal  (soc.  Figs.  8,  9,  15;  Pis.  XIX, 
XX,  XXI,  XXIII)  has  in  its  present  state  of  preservation  its  an- 
terior end  at  the  anterior  border  of  the  bone-plate  Llt  but  in  the  living 
fish  it  continued  forward  into  the  soft  tissue  anteriorly  and  laterally 
to  this  plate.    How  it  may  have  passed  in  this  soft  tissue  it  is  of  course 


Macropetalichthyids  and  other  Arthrodires — Stensio     147 

not  possible  to  say  positively,  but  it  seems  to  me  most  probable  that 
it  was  there  as  in  Coccostens,  and  forms  allied  to  this  (Cf.  Jaekel  1902 
fig.  to  page  107;  1906a,  text  figs.  2,  3),  i.e.,  that  it  very  soon  turned 
backwards  and  went  dorsally  and  behind  the  nasal  opening  down  to 
the  infraorbital  canal.  It  would  thus,  if  I  am  right,  have  had  the 
same  course  in  its  anterior  parts  as  in  Elasmobranchs.  (Cf.  Garman 
1888;  Allis  1901,  pp.  104-107,  1 18-128;  1905,  p.  419,  pp.  470-478; 
1923;  Ewart  1892,  pp.  66-74;  Hawkes  1906,  pp.  960-961,  PI.  68;  cf. 
also  Cole  1896  a,  b.)  Within  the  bone-plate  Lx  it  runs  first  backward 
and  slightly  laterally  to  about  the  center  of  the  ossification  of  the  plate, 
then  fairly  suddenly  curves  and  takes  a  backward  and  slightly  medial 
direction.  With  this  direction  it  continues  backward  to  the  plate  M2, 
which  it  traverses  to  about  the  center  of  ossification,  and  here  joins  its 
fellow  of  the  opposite  side  and  a  cross  comissural  sensory  canal  between 
the  cephalic  division  of  the  lateral  lines  in  the  way  shown  in  text  fig. 
15.  No  anastomosis  is  found  between  it  and  the  posterior  part  of  the 
infraorbital  canal  of  its  side. 

To  the  supraorbital  sensory  canal  go  several  fine  branches  from 
the  canal  for  the  n.  ophthalmicus  lateralis.  The  number  of  these 
branches  could  not,  however,  be  established.  The  posterior  ones  issue 
dorso-postero-medially,  the  anterior  ones  antero-dorso-laterally.  In 
Pis.  XXI  and  XXIII  one  anterior  branch  (rm.ophth.lat)  is  clearly 
seen  issuing  from  the  canal  for  the  n.  ophthalmicus  lateralis  (c.ophth. 
lat)  to  the  supraorbital  sensory  canal  (soc). 

Its  considerable  extension  backwards  and  its  direction  in  the  pos- 
terior parts,  indicate  with  certainty  that  the  supraorbital  sensory  canal 
comprises  not  only  the  supraorbital  sensory  canal  as  found,  for  in- 
stance, in  Amia  and  many  other  fishes,  but  also  the  homologue  of  the 
anterior  head  line  of  pit  organs  of  these  fishes.  (Cf.  Allis  1889,  pp. 
505-506;  1900,  pp.  445;  1903,  p.  187;  1905;  Herrick  1901,  pp.  222- 
223;  Stensio  1921,  pp.  218,  263;  1922,  p.  192;  1923,  p.  1258;  1925.) 

The  infraorbital  sensory  canal  (ifc,  Figs.  8,  15;  Pis.  XIX,  XX, 
XXII;  PI.  XXIV,  fig.  1)  has  its  posterior  end  situated  at  about 
the  ossification  center  of  the  plate  P2;  being  there  continuous  with  the 
cephalic  division  of  the  lateral  line  of  its  side.  From  this  place  it  runs 
forward  and  slightly  medially  into  the  plate  Plt  retaining  the  same  di- 
rection as  behind  this  and  being  during  this  part  of  its  course  situated 
latero-ventrally  of  the  orbital  opening.  It  does  not,  however,  traverse 
the  bone-plate  Px,  in  the  entire  length,  but  goes  to  the  lateral  border 
of  this  some  distance  behind  the  anterior  end  as  is  shown  in  text  fig. 
15.     After  leaving  the  cranial  roof  at  this  point,  it  must  have  passed 


148    Field  Museum  of  Natural  History — Geology,  Vol.  IV. 

forward  and  downward  on  the  cheek,  probably  through  soft  tissue,  and 
it  is  likely  that  it  extended  as  far  forward  as  to  the  rostrum,  and,  that 
it,  as  pointed  out,  anastomized  with  the  supraorbital  canal  behind  the 
nasal  opening. 

To  the  part  of  the  infraorbital  canal  situated  within  the  bone- 
plates  P1  and  P2  lead  a  few  fine  canals  which  pierce  the  lateral  parts 
of  the  postorbital  process  and  which  very  probably  transmitted  lateralis 
branches  from  a  nerve  corresponding  to  the  r.  oticus  lateralis  of  recent 
fishes.  Two  of  these  branches  (in)  are  partly  seen  in  Pis.  XX,  XXII, 
and  it  is  easy  to  understand  from  their  direction  that  they  in  any  case 
must  have  been  traversed  by  lateralis  branches  that  were  given  off  from 
a  prootic  nerve,  i.e.,  a  nerve  that  had  its  exit  through  the  cranial  wall 
anterior  to  the  labyrinth. 

Before  leaving  the  infraorbital  canal,  it  is  finally  necessary  to  point 
out  that  its  course  in  the  dermal  cranial  roof  is  incorrect  in  the  restora- 
tion published  by  Dean  (1901,  text  fig.  12). 

The  cephalic  division  of  the  lateral  line  (Ic,  text  figs.  4,  15;  Pis. 
XIX,  XX,  XXIV)  enters  the  dermal  cranial  roof  at  the  posterior 
border  of  the  bone-plate  S,  traverses  this  bone-plate  in  anterior  and 
slightly  medial  direction,  and  continues  with  the  same  direction  to  the 
ossification  center  of  the  bone-plate  L3.  There  it  suddenly  takes  an 
antero-lateral  course  and  goes  with  this  to  the  ossification  center  of  the 
bone-plate  P2,  joining  there,  as  already  mentioned,  the  infraorbital  canal. 

At  the  place  in  the  bone-plate  L,,  where  the  cephalic  division  of 
the  lateral  line  turns  laterally,  it  gives  off  an  antero-medial  branch 
which  goes  to  the  ossification  center  of  the  plate  M2,  joining  there  with 
its  fellow  of  the  opposite  side  and  forming  in  this  way  an  angulated 
transverse  commissure  (c.pp,  text  figs.  4,  15;  Pis.  XIX,  XX;  PI. 
XXIV,  fig.  3).  At  the  angle  in  the  median  line  this  commissure 
anastomozes  with  the  posterior  end  of  the  supraorbital  sensory  canals 
just  after  these  have  joined  one  another. 

A  short  anterior  portion  of  the  cephalic  division  of  the  lateral  line 
just  behind  the  infraorbital  sensory  canal  was  probably  innervated  by 
the  presumed  lateralis  branch  that  traversed  the  cranial  wall,  together 
with  the  n.  glossopharyngeus.  The  remaining  part  of  the  division 
anterior  of  the  transverse  commissure,  as  well  as  the  adjacent  half 
of  this  commissure,  was  supplied  by  a  nerve  that  issued  from 
the  n.  linese  lateralis  already  within  the  vagus  canal  and  from  there 
went  upward  through  the  canal  dx,  (PL  XXIV,  fig.  2),  and  its 
branches  dxa  and  dxb  (PL  XXIV,  fig.  2),  thus  by  a  ramus  supra- 
temporalis  from  the  n.  lineae  lateralis.    Finally,  the  part  of  the  division 


Macropetalichthyids  and  other  Arthrodires — Stensio     149 

behind  the  transverse  commissure  was  innervated  by  a  number  of  fine 
branches  which  independently  of  each  other  issued  from  the  n.  lineae 
lateralis,  each  of  them  probably  supplying  only  a  single  sense  organ. 
In  the  anterior  division  of  the  occipital  region  where  these  nerve 
branches  pierced  the  primordial  neurocranium,  six  of  these  canals  are 
seen  in  the  Field  Museum  specimen  (Id^ld*  Pis.  XIX,  XX ;  PI.  XXIV, 
fig-  3). 

In  the  description  of  the  anterior  division  of  the  occipital  region  it 
was  pointed  out  that  a  fine  branch  from  the  n.  lineae  lateralis  prob- 
ably went  up  to  the  dorsal  surface  of  the  primordial  neuro- 
cranium through  the  canal  cl  (text  fig.  3;  Pis.  XIX,  XX).  This  fine 
lateralis  branch  thus  had,  if  it  really  existed,  such  a  course  that  it 
must  have  innervated  one  or  a  few  sensory  canal  organs  situated 
medially  of  the  cephalic  division  of  the  lateral  line  posterior  to  the 
cross  commissural  canal  c.pp,  but,  as  it  is  not  a  closed  sensory  canal 
there,  the  presumed  sensory  canal  organs  supplied  by  it  would  have 
formed  a  short,  transverse  pit-line.  Unfortunately  the  material  inves- 
tigated did  not  enable  me  to  decide  whether  there  was  a  groove  for 
such  a  pit-line  on  the  dorsal  side  of  the  dermal  bones.  The  possible 
non-existence  of  the  groove  need  not,  however,  indicate  absolutely 
the  absence  of  the  pit-line,  for  this  may  in  such  a  case  very  well  be 
thought  to  have  been  situated  entirely  in  the  skin  and  thus  to  have 
been  wholly  unrelated  to  the  underlying  dermal  bones. 

If  the  pit-line  in  question  really  could  be  shown  to  exist,  it  would, 
according  to  its  position  and  innervation,  evidently  be  homologous  with 
the  supratemporal  commissure  in  recent  fishes,  while  the  cross  com- 
missural canal  c.pp  would  represent  the  posterior  head  line  of  pit  organs 
in  these,  a  view  which  is  also  supported  by  the  position  and  direction 
of  each  half  of  the  latter  canal.  (Cf.  Allis  1889,  PI.  42 ;  1901,  pp.  101- 
103,  116-117,  PI.  10;  1903,  pp.  186-187,  PI.  Ill;  1905,  pp.  471,  474; 
Ewart  1892,  PI.  II,  fig.  2;  Stensio  1923,  p.  1258,  fig.  4.)  Below, 
in  the  description  of  Epipetalichthys,  we  shall  find  additional  facts 
which  point  in  the  same  direction. 

According  to  the  restoration  published  by  Dean  (1901,  text  fig. 
12)  a  canal,  which,  in  its  position,  corresponds  very  well  to  the 
preopercular  canal,  issues  in  latero-ventral  and  slightly  posterior  di- 
rection from  the  point  where  the  infraorbital  canal  joins  the  cephalic 
division  of  the  lateral  line.  This  canal  is  not  found  in  Eastman's 
restorations  in  1908  (Eastman  1908a,  text  fig.  19;  1908b,  text  fig.  24), 
and  the  material  investigated  by  me  was  not  preserved  sufficiently  well 
to  show  with  certainty  whether  Dean  or  Eastman  is  right  in  this 


150    Field  Museum  of  Natural  History — Geology,  Vol.  IV.  , 

respect.  As  the  canal  in  question  is  found  in  a  specimen  described  as 
Macro pctalichthys  agassizif  below,  and  also  occurs  in  most  other 
Arthrodires,  it  seems  very  likely  that  it  is  not  missing  in  Macropeta- 
lichthys  rapheidolabis.  On  account  of  this  it  was  drawn  in  text  fig.  15, 
in  which  it  is  designated  by  the  letters  foe.  If.  it  really  was  present,  it 
must  have  continued  down  to  -the  cheek,  where  it  chiefly,  or,  perhaps, 
even  entirely,  had  its  passage  through  soft  tissue. 

REMARKS   ' 

On  account  of  the  flat,  broad  shape  of  the  primordial  neurocranium 
as  a  whole  and  the  position  and  direction  of  the  orbital  openings,  there 
can  be  no  doubt  that  M.  rapheidolabis,  like  other  species  of  Macropeta- 
lichthys  must  have  been  a  decided  benthonic  form. 

The  description  given  here  makes  it  fully  evident  that  many  of  the 
strange  anatomical  features  which  Eastman  thought  he  had  observed 
in  M.  rapheidolabis  are  mistakes. 

MACROPETALICHTHYS  AGASSIZI?     (H.  v.  Meyer) 
(PI.  XXIX,  figs,  i,  2) 

Through  the  courtesy  of  Mr.  S.  Junkermann  of  Bielefeld,  Ger- 
many, I  had  the  opportunity  of  examining  an  imperfectly  preserved 
neurocranium  of  a  Macropetalicthyid,  which,  as  far  as  it  is  preserved, 
agrees  so  well  with  M.  rapheidolabis,  that  it  at  least  provisionally  seems 
correct  to  refer  it  to  the  genus  Macro  pctalichthys.  Among  the  species 
described  so  far  of  this  genus  it  seems  to  resemble  most  closely  M. 
agassizi,  and  on  this  account  I  have,  with  some  hesitation  given  it  this 
specific  name. 

The  primordial  neurocranium  is  imperfectly  preserved,  being  rep- 
resented only  by  certain  parts  of  the  occipital  region  (PI.  XXIX,  fig. 
1),  which  are  much  fractured  and  crushed.  As  far  as  can  be  seen, 
it  seems  to  have  been  less  ossified  than  that  of  M.  rapheidolabis,  but 
at  least  in  the  posterior,  narrow  division  of  the  occipital  region,  I  found 
both  the  internal  and  external  bone  layers.  Further  forward  the  in- 
ternal bone  layer  appears  to  have  been  entirely  lacking.  With  regard 
to  its  general  shape,  the  primordial  neurocranium  seems  to  have  con- 
siderably resembled  that  in  M.  rapheidolabis. 

In  text  fig.  16  we  see  two  transversal  sections  through  the  most 
anterior  part  of  the  posterior  narrow  division  of  the  occipital  region. 
As  is  evident  from  these  sections,  the  haemal  groove  did  not  extend  so 
far  forward  as  in  M.  rapheidolabis,  and  it  is  further  worthy  of  notice, 
that,  contrary  to  what  is  the  case  in  that  species,  there  was  no  bone 


Macropetalichthyids  and  other  Arthrodires — Stensio     151 

tube  around  the  notochord.  In  the  anterior  one  of  the  two  sections 
figured,  the  postero-lateral-dorsal  corners  of  the  anterior  broad  division 
of  the  region  are  seen  in  section,  as  they  are  extended  considerably  in 
postero-lateral  direction  (pr,  text  fig.  16a).  Of  the  dermal  cranial 
roof  we  find  the  plates  M2,  L3,  P%  and  5"  (text  fig.  16a;  PI.  XXIX, 
fig.  2)  more  or  less  well-preserved.  Their  ornaments  consist  of  small, 
numerous,  rather  densely  placed  tubercles,  which  are  stellate  at  their 
bases. 

The  sensory  canals  are  closed  tubes  situated  deeply  in  the  dermal 
bones,  as  in  M.  rapheidolabis.  They  open  outward  with  numerous, 
straight,  unbranched  tubuli,  but  while  these  tubuli  in  M.  rapheidolabis 
are  arranged  in  a  double  series,  they  form  here  only  a  single  one  from 
each  canal  (PI.  XXIX,  fig.  2).    It  is  quite  probable  that  the  canals  for 


,cr.od 


«—  er.ol 


Fig.  16.     Macropetalichthys  agassizi? 


Transverse  section  through  the  most  anterior  part  of  the  posterior  narrow 
division  of  the  occipital  region.  The  section  A  taken  only  a  short  distance  an- 
terior to  the  section  B.  Cartilage  dotted,  layers  of  substitution  bone  with  strong 
black  lines,  dermal  bones  of  the  cranial  roof  with  vertical  striation.     X'/s 

cr.od,  crista  occipitalis  dorsalis ;  cr.ol,  crista  occipitalis  lateralis ;  ch,  probable 
position  of  the  space  for  the  notochord ;  cv,  cavum  cerebrale  cranii ;  Ic,  cephalic 
division  of  the  lateral  line;  pr,  postero-laterally  projecting  corner  of  the  anterior 
broad  division  of  the  occipital  region. 

nerves  leading  from  below  to  the  sensory  canals  were  much  fewer  in 
number  than  the  tubuli,  a  fact  which  enables  us  to  conclude  with  a 
rather  great  degree  of  probability,  that  the  sensory  canal  organs  did 
not  correspond  in  number  to  the  tubuli  but  were  much  less  numerous 
than  these. 


152     Field  Museum  of  Natural  History — Geology,  Vol.  IV. 

MACROPETALICHTHYS  PELMENSIS,  Hennig 

The  description  given  by  Hennig  (1907)  of  this  species  is,  as  I 
found  by  examination  of  his  type  specimen,  in  several  respects  very 
incorrect. 

What  Hennig  (1907,  pp.  585-586)  takes  to  be  a  paired  lateral 
occipital  seems  in  fact  to  be  a  ventral,  paired  process  from  the  bone- 
plate  S,  of  the  dermal  cranial  roof,  according  to  the  terminology  em- 
ployed by  me  in  the  present  paper.  This  process,  which  meets  its 
fellow  of  the  opposite  side  in  a  median  suture  and  extends  very  low 
downwards,  covers  the  posterior  surface  of  the  probably  very  large 
cranio-spinal  process  of  its  side. 

The  structure  of  the  dermal  cranial  roof  was  also  in  other  respects 
very  much  misinterpreted  by  Hennig,  a  circumstance  which  is,  how- 
ever, so  obvious  that  it  will  not  be  necessary  to  deal  with  it  here. 

Eastman's  description  of  the  species  in  1908  (1908b,  pp.  176-177) 
is,  with  regard  to  the  posterior  parts  of  the  neurocranium,  also  very 
erroneous,  as  Eastman  on  that  occasion  did  not  even  correctly  recog- 
nize the  main  divisions  of  the  neurocranium,  a  fact  which  lead  him  to 
certain  very  strange  conclusions  about  the  position  of  the  ductus  endo- 
lymphaticus  and  the  relations  between  this  and  the  sensory  canal  sys- 
tem (Cf.  Kaer  1915,  pp.  11-12). 

It  may  finally  be  emphasized  in  this  connection  that  the  primordial 
neurocranium  probably  is  preserved  in  the  specimen,  and  that  a  further 
preparation  of  it  would  therefore  be  very  desirable. 

EPIPETALICHTHYS  WILDUNGENSIS,  Jaekel,  gen.  nov.,  sp.  nov. 

PI.  XXVIII,  figs.  1,  2;  PI.  XXIX,  figs.  3,  4;  PI.  XXX,  fig.  1; 
PI.  XXXI,  fig.  2. 

This  species,  which  is  a  new  one  and  also  represents  a  new  genus, 
is  from  the  upper  Devonian  of  Wildungen,  Germany.  It  was  placed 
at  my  disposal  by  Professor  O.  Jaekel  of  Greifswald.  On  the  labels 
accompanying  it  Professor  Jaekel  had  named  it  Epipetalichthys  wild- 
ungensis.  So  far,  only  a  single  specimen,  represented  by  the  imper- 
fectly preserved  neurocranium,  has  been  found  of  it.  To  Judge  from 
this  specimen,  the  species  must  have  attained  about  the  same  size  as 
Macro  pet  alichthys  rapheidolabis. 

PRIMORDIAL   NEUROCRANIUM 
General  remarks.     The  primordial  neurocranium,  if  we  first  turn 
to  this,  is  partly  rather  badly  crushed  and  fractured,  and,  in  addition, 
also,  weathered  in  places,  so  that  it  is  not  by  far  as  well  adapted  for  a 


Macropetalichthyids  and  other  Arthrodires — Stensio     153 

detailed  examination  as  that  in  the  Field  Museum  specimen  of  Macro- 
petalichthys  rapheidolabis.  In  its  general  shape  it  must  obviously  have 
resembled  that  of  the  last-mentioned  species,  but,  as  we  shall  see,  it 
differs  distinctly  from  this  in  certain  details. 

Its  degree  of  ossification  was  considerably  less  than  that  in  M. 
rapheidolabis  and  less  also  than  in  M.  agassisif,  a  fact  which  deserves 
a  special  attention,  as  we  are  here  concerned  with  an  upper  Devonian 
form,  while  the  other  two  just  mentioned  specimens  are  both  from 
earlier  divisions  of  the  Devonian.  At  least  this  is  beyond  question  the 
case  with  M.  rapheidolabis,  which  occurs  only  in  middle  Devonian  strata. 

On  account  of  the  imperfect  state  of  preservation  in  which  the 
primordial  neurocranium  is  found,  it  is  not  possible  to  make  out  with 
full  exactness  the  extension  of  its  different  layers  of  substitution  bone, 
but  the  following  may  give  an  idea  of  the  most  important  differences 
from  M.  rapheidolabis  in  this  respect. 

1.  There  is  no  evidence  of  the  labyrinth  bone  layer.  2.  The  inner 
bone  layer  seems  to  be  entirely  lacking,  except  in  the  posterior,  narrow 
division  of  the  occipital  region  (text  fig.  17).  3.  The  external  bone 
layer  surrounds  the  posterior,  narrow  division  of  the  occipital  region, 
and  extends  from  this  forward  also  on  to  the  lateral  and  ventral  sides  of 
the  anterior  division  of  the  same  region  and  the  ventral  side  of  the 
labyrinth  region.  Whether,  however,  it  continued  from  the  latter  region 
to  the  ventral  side  of  the  orbitotemporal  region,  cannot  be  decided,  as 
the  ventral  parts  of  this  region  have  been  destroyed.  On  the  ethmoidal 
region  it  is,  however,  found  again  on  the  ventral  side  and,  in  addition, 
at  least  partly,  on  the  lateral  sides  and  probably  also  on  the  anterior 
end.  Accordingly,  it  is  lacking  on  the  larger  anterior  part  of  the  dorsal 
side,  quite  as  in  M.  rapheidolabis,  but,  contrary  to  what  is  the  case  in 
that  form,  also  probably  on  the  lateral  sides  of  the  entire  labyrinth  and 
orbitotemporal  regions  and  the  posterior  side  of  the  ethmoidal  region. 
If  it  was  lacking  on  the  ventral  side  of  the  orbitotemporal  region,  this 
region  would  obviously  have  consisted  entirely  of  cartilage.  4.  The 
canal  layers  seem  to  have  become  entirely  reduced. 

As  far  as  I  can  see,  there  are  no  traces  of  ossification  centers  either 
in  the  occipital  region  or  in  the  ethmoidal  region. 

Microscopic  Structure  of  the  Bone 
The  substitution  bone  of  M.  rapheidolabis  has  generally  been  much 
infiltrated  by  a  dark  bitumen  that  is  difficult  to  remove,  and,  accord- 
ingly, no  good  microscopic  sections  can  be  made  from  it.  I  could, 
however,  see  rather  distinctly  that  it  has  numerous  cell  spaces  (PI. 
XXXI,  fig.  1).     In  the  species  under  consideration  the  bone  tissue  is 


i54    Field  Museum  of  Natural  History — Geology,  Vol.  IV. 

also  not  favorably  preserved  for  microscopic  investigation,  but  it  is 
fully  obvious  that  it  there  too  contained  cell-spaces  in  fairly  large 
number.  In  the  posterior  division  of  the  occipital  region  we  can 
further  see  that  from  the  external  and  internal  bone  layers,  numer- 
ous, irregular  trabecular  (PI.  XXXI,  fig.  2)  extend  a  short  distance 
into  the  parts  of  the  cranial  walls  that  were  occupied  by  cartilage,  so 
that  there  really  is  certain  evidence  of  cancellous  bone,  although  this 
bone  was  very  slightly  developed.  By  means  of  short  bone  trabecular 
of  about  the  same  kind  as  those  just  mentioned,  the  bone  layer  sur- 
rounding the  notochordal  space  (ch.l,  PI.  XXXI,  fig.  2)  is  connected 
with  the  internal  and  external  bone  layers.  Otherwise,  no  details  can 
be  observed. 

Occipital  Region 

As  in  M.  rapheidolabis  and  M.  agassizi?  the  occipital  region  is 
composed  of  two  divisions,  a  posterior,  long  and  narrow  one,  and  an 
anterior,  short  and  broad  one. 

ft 


A  cent 

Fig.  17.    Epipetalichthys  wildungensis  Jaekel 

Transverse  section  through  the  anterior  half  of  the  posterior  division  of  the 
occipital  region.  Layers  of  substitution  bone  with  strong  black  lines,  cartilage 
dotted.  The  trabecular  of  substitution  bone  penetrating  inwards  into  the  cartilage 
from  the  bone  layers  not  drawn.     XVs 

ham,  haemal  groove;  ch,  space  for  the  notochord;  cv,  cavum  cerebrale  cranii. 

The  posterior  one  (text  fig.  18;  PI.  XXVIII,  fig.  2)  is  represented 
merely  by  an  anterior  part,  and  no  certain  statement  can  therefore  be 
given  of  its  length.  It  is  narrow  and,  contrary  to  that  in  M.  rapheido- 
labis and  M.  agassizi f,  it  equals  the  other  divisions  of  the  primordial 
neurocranium  in  height.  Further,  it  differs  from  that  in  the  two  species 
mentioned  in  the  fact  that  it  does  not  have  the  slightest  traces  of  the 
crista  occipitalis  lateralis,  which  in  them  is  such  an  important  feature. 
The  haemal  groove  (hcem,  text  figs.  17,  18;  PI.  XXVIII,  fig.  2)  is 
rather  distinct  and  it  is  noteworthy  that  we  find  in  the  part  of  it  pre- 


Macropetalichthyids  and  other  Arthrodires — Stensio     155 

served  two  rather  shallow  depressions  (seen  in  text  fig.  18),  which, 
perhaps,  may  be  segmentally  arranged.  Otherwise  I  only  wish  to 
emphasize  that  the  division  was  narrowest  anteriorly  at  the  transition 
to  the  anterior  division,  gradually  increasing  somewhat  in  breadth  back- 
ward from  this  place. 

A  transverse  section  through  the  part  of  the  division  present  (text 
fig.  17)  shows  that  the  cavum  cerebrale  cranii  (cv)  within  this  part 
was  very  high  and  narrow  and  that  there  was  below  the  cavum  cere- 
brale a  space  for  the  notochord  (ch).  This  space  is,  like  that  in  Macro- 
pctalichthys  raphcidolabis,  bounded  by  a  bone  layer  of  its  own,  a  bone 
layer  that  is  continuous  dorsally  with  the  inner  bone  layer  (bottom  of 
the  cranial  cavity),  and  ventrally  with  the  external  bone  layer  (bottom 
of  the  haemal  groove),  as  already  pointed  out  above  (PI.  XXXI,  fig.  2). 

No  traces  of  canals  for  spino-occipital  nerves  could  be  seen  in  the 
part  of  the  division  present. 


--i--c.rv.1 


Fig.  18.    Epipetalichthys  wildungensis 

A  posterior  part  of  the  primordial  neurocranium  from  the  central  side.     X$4- 
c.rai,  c.rat,  anterior  and  posterior  openings  respectively  of  the  canal  for  the  radix 

aorta:    (lateral  dorsal  aorta);   ham,  haemal  groove;   s.ra,  groove    for  the  radix 

aortae  lateral  dorsal  aorta,  anterior  of  the  canal  era. 

Of  the  anterior  broad  division  of  the  region  only  the  ventral  parts 
are  accessible  for  investigation  (text  fig.  18;  PI.  XXVIII,  fig.  2).  As 
far  as  can  be  seen  from  these  its  shape  must  have  been  very  much  the 
same  as  in  Macropetalichthys  rapheidolabis. 

With  regard  to  the  details,  we  find  that  in  this  division  the  pos- 
terior part  of  the  groove  for  the  radix  aortae  forms  a  closed  canal  in 
the  primordial  neurocranium.  This  canal  has  its  anterior  and  posterior 
openings  (c.ralt  c.ra2)  situated  as  shown  by  text  fig.  18  and  PI.  XXVIII, 
fig.  2. 

Nothing  is  so  far  known  concerning  the  vagus  canal  and  its  branches. 

Labyrinth  and  Orbitotemporal  Region 
The  labyrinth  region  (PI.  XXVIII,  fig.  2)  is  somewhat  longer  than 
in  M.  rapheidolabis.    It  is  very  fragmentarily  preserved,  only  parts  of 
the  external  bone  layer  of  its  ventral  side  being  left. 


156     Field  Museum  of  Natural  History — Geology,  Vol.  IV. 

The  orbitotemporal  region  is  still  more  imperfectly  preserved,  and 
the  only  statement  that  can  be  made  about  it  is  that  it  certainly  was 
rather  short  and  that  the  orbits  are  situated  far  apart  and  in  such  a 
way  that  the  eyes  must  have  been  directed  much  upwards,  quite  as  in 
M.  rapheidolabis. 

Ethmoidal  Region 

On  account  of  the  fact  that,  as  pointed  out,  it  has  the  external  bone 
layer  persisting  to  a  considerable  extension,  the  ethmoidal  region  has 
been  fairly  well  preserved.  A  large  part  of  its  ventral  side,  an  anterior 
part  of  its  lateral  side,  an  anterior  part  of  its  dorsal  side  and  the 
anterior  end  are  available  for  investigation  (text  fig.  19;  PI.  XXVIII, 
fig.  1;  PI.  XXIX,  fig.  3;  PI.  XXX,  fig.  1). 

From  its  broad,  posterior  end,  it  becomes  rapidly  narrow  forward, 
but  does  not  taper  to  a  point,  its  anterior  end  being  truncated  and 
rather  concave.  The  breadth  at  this  end  is  about  one-third  of  that  at 
the  posterior  end. 

From  the  antero-ventral  part  of  each  lateral  side  the  olfactory  cap- 
sule (olf,  text  fig.  19;  PI.  XXIX,  fig.  3;  PI.  XXX,  fig.  1)  projects 
laterally  exactly  as  in  M.  rapheidolabis.  Unfortunately  it  is  not  so  well 
preserved  as  in  that  species,  its  anterior  and  external  parts  being  prac- 
tically destroyed,  and  on  account  of  this  nothing  can  be  said  with  cer- 
tainty about  its  external  opening  and  whether  there  was  any  nasal  fon- 
tanels on  the  ventral  side  of  its  lateral  part. 

The  ventral  surface  of  the  region  (PI.  XXIX,  fig.  3)  is  rather 
concave  in  transversal  direction  and  has  in  the  postero-lateral  part 
somewhat  medially  of  the  lateral  margin  a  longitudinal,  shallow  groove 
(s.pal)  for  the  r.  palatinus  facialis,  quite  as  in  M.  rapheidolabis.  Each 
one  of  the  lateral  surfaces  (PI.  XXVIII,  fig.  1),  is  concave  in  dorso- 
ventral  direction,  and  has  a  long  post-nasal  portion  as  in  M.  rapheidola- 
bis. The  dorsal  surface  (text  fig.  19;  PI.  XXX,  fig.  1)  is  exposed 
only  most  anteriorly,  the  most  anterior  of  the  bones  in  the  dermal 
cranial  roof  being  weathered  away.  We  find  in  this  part  of  it  a  very 
deep,  anteriorly  and  dorsally  open  depression  (pfg),  which,  as  far  as 
can  be  judged  from  the  conditions  in  the  fossil,  seems  to  have  been 
lined  by  the  external  bone  layer. 

This  depression,  which,  as  already  pointed  out  in  the  description 
of  M.  rapheidolabis,  is  obviously  the  homologue  of  the  similarly 
situated  depression  in  the  skulls  of  Elasmobranchs,  and  which  therefore 
may  be  properly  called  the  cavum  precerebrale,  was,  contrary  to  that 
in  these  fishes,  separated  from  the  cavum  cerebrale  by  a  thick  septum 
of  cartilage,  presumably  lined  with  the  external  bone-layer  on  the  an- 


Macropetalichthyids  and  other  Arthrodires — Stensio     157 

terior  side.  There  is  thus  no  fenestra  precerebralis.  Laterally  the 
cavum  cerebrale  is  also  well  separated  from  the  nasal  capsules.  Its 
floor  is  not  perforated  by  any  foramina. 

Cavum  Cerebrale 

Since  the  internal  bone  layer,  as  pointed  out,  is  lacking-,  except  in 
the  posterior  division  of  the  occipital  region,  the  shape  of  the  cavum 
celebrale  is  known  merely  in  this,  where  it,  as  seen  from  text  fig.  17, 
is  very  high  and  narrow. 

The  canal  for  the  pineal  and  parietal  organs  seems  not  to  have  per- 
forated the  dermal  bones  of  the  cranial  roof.  At  least  no  traces  of 
such  a  perforation  could  be  seen  in  the  parts  of  the  dermal  bones 
preserved. 

DERMAL  BONES  OF  THE  CRANIAL  ROOF 

Parasphenoid  or  other  dermal  bones  were  not  present  on  the  ven- 
tral side  of  the  primordial  neurocranium. 

The  dermal  bones  of  the  dorsal  side  .of  the  primordial  neurocranium 
(text  fig.  19;  PI.  XXX,  fig.  1)  are  the  same  as  in  M.  rapheidolabis, 
and  their  extensions  and  relations,  too,  are  about  the  same  as  in  this, 
with  the  exception,  however,  that  the  plates  Mt  and  M2  do  not  meet, 
but  are  separated  by  the  plates  Llf  which  extend  to  and  suture  with 
one  another  in  the  median  line. 

The  plate  Ls  is,  in  the  posterior  part,  perforated  by  a  rather  large, 
oblong  foramen  (d.end),  which  certainly  must  be  the  external  opening 
of  the  canal  for  the  ductus  endolymphaticus.  This  foramen  lies  defin- 
itely behind  the  place  where  in  M.  rapheidolabis  the  fossa  endolym- 
phatica  is  situated,  and  it  seems  therefore,  rather  probable  that  the  duc- 
tus endolymphaticus  from  this  fossa  extended  somewhat  backward  be- 
neath the  dermal  cranial  roof,  thus  making  a  bend  and  continuing  back- 
ward quite  as  it  does  in  Chlamydoselachus  (Goodey  1910,  PI.  43,  figs. 
7,  8)  and  several  other  Elasmobranchs  (Retzius  1881).  In  this  con- 
nection it  deserves  also  to  be  emphasized  that  the  position  of  the  ex- 
ternal opening  of  the  ductus  endolymphaticus  in  the  form  under  con- 
sideration has,  in  relation  to  the  sensory  canal  system,  exactly  the  same 
position  as  in  Chlamydoselachus  (Cf.  Allis  1923,  PI.  II).1 

The  ornament  on  the  dermal  bones  of  the  cranial  roof  consists  of 
short,  rather  low,  but  nevertheless  distinct,  ridges,  which,  on  the  plates 
5"  and  M2,  seem  to  lie  with  their  longitudinal  axis  about  parallel  with 

1In  Chlamydoselachus  the  ductus  endolymphaticus  has  its  external  opening 
posterior  of  the  supratemporal  commissure  of  the  main  lateral  lines;  in  Acanthias, 
Mustelus  and  others,  on  the  contrary,  it  has  this  opening  anterior  of  the  same 
commissure  (Cf.  Allis  1901,  PI.  10). 


158    Field  Museum  of  Natural  History — Geology,  Vol.  IV. 

the  longitudinal  axis  of  the  head.  On  the  other  bones,  excepting  the 
plate  Mlt  on  which  their  arrangement  is  unknown,  the  ridges  are,  on 
the  contrary,  arranged  concentrically  with  the  edges  of  the  bones  (PL 
XXIX,  fig.  4).  In  the  Macropetalichthys  species  known  so  far,  the 
ornament  consists  of  fairly  sparse  tubercles,  which  are,  in  the  main, 
irregularly  scattered. 

THE  SENSORY  CANALS  OF  THE  HEAD 
The  sensory  canals  of  the  head  are  known  merely  in  the  bones  of 
the  dermal  cranial  roof,  in  which  they  form  closed  canals.     They  are 
finer  than  in  M.  rapheidolabis ;  and  the  ridges  for  them  on  the  lower 

Pff 


Fig.  19.    Epipetalichthys  wildungensis 

Head  in  dorsal  view  with  the  anterior  parts  of  the  bone  plate  Mi  removed  to 
show  the  cavum  precerebrale.  The  sensory  canals  marked  with  dotted  outlines 
and  colours.     XJ4- 

Li,  L2,  L3,  Mi,  Mi,  Pi,  P2,  S,  dermal  bones  of  the  cranial  roof  (the  anterior 
larger  part  of  the  plate  Mi,  removed)  ;  d.cnd,  external  opening  of  the  canal  for 
the  ductus  endolymphatic^ ;  ifc,  infraorbital  sensory  canal  (blue);  Ic,  cephalic 
division  of  the  main  lateral  line  (red);  na,  nasal  aperture;  olf,  nasal  capsule; 
orb,  orbital  entrance ;  pfg,  cavum  precerebrale ;  st.com,  supratemporal  commissure 
between  the  cephalic  division  of  the  main  lateral  lines  (red)  ;  soc,  supraorbital 
sensory  canal   (green). 


Macropetalichthyids  and  other  Arthrodires — Stensio     159 

sides  of  the  bones  are  also  less  strong  than  in  that  species.  They 
open  outwards  with  numerous  short  and  generally  unbranched  tubuli 
(PI.  XXX,  fig.  1),  which,  however,  contrary  to  the  case  in  M.  rapheido- 
labis  are  arranged  like  those  in  M.  agassisi?  and  M.  pelmensis  in  a 
single  series. 

The  supraorbital  sensory  canal  (soc,  Fig.  19;  PI.  XXX,  fig.  1) 
does  not  extend  as  far  backwards  as  in  M.  rap  held  olabis,  and,  on  this 
account,  does  not  meet  its  fellow  of  the  opposite  side  in  the  median 
line  nor  does  it  anastomose  with  the  commissure  (s.com)  between  the 
cephalic  divisions  of  the  main  lateral  lines,  but  ends  some  distance 
anterior  of  this.  Behind  the  part  where  it  ends  as  a  closed  canal  it 
may,  however,  probably  have  continued  a  short  distance  further  back- 
wards as  a  pit  line.  Its  anterior  parts  are  not  known,  but  it  seems 
very  probable  that  anterior  of  the  most  anterior  part  preserved  in  the 
fossil  it  curved  strongly  backwards  and  went  first  dorsally  and  then 
posteriorly  of  the  nasal  opening  down  to  the  infraorbital  sensory  canal, 
as  it  does  in  Coccosteus  and  Elasmobranchs.  All  the  tubuli  of  the 
preserved  portion  of  the  canal  issue  in  lateral  direction,  as  is  clearly 
shown  by  PI.  XXX,  fig.  1. 

The  infraorbital  sensory  canal  (ifc,  Fig.  19;  PI.  XXX,  fig.  1) 
is,  in  the  main,  as  in  M.  rapheidolabis. 

The  cephalic  division  of  the  lateral  line  (Ic,  Fig.  19)  ;  PI.  XXX, 
fig.  1)  has  also  the  same  course  as  in  M.  rapheidolabis,  and  is,  as  in 
this,  in  communication  with  its  fellow  of  the  opposite  side  by  a  trans- 
versal commissure  (st.com,  Fig.  19;  PI.  XXX,  fig.  1),  which 
traverses  the  plate  L3  and  the  plate  M2  to  the  plate  L3  of  the  opposite 
side.  This  commissure  is,  however,  contrary  to  that  in  M.  rapheidolabis, 
almost  straight,  and,  as  already  mentioned,  it  does  not  communicate  with 
the  posterior  ends  of  the  supraorbital  canals.  It  seems  even  to  be 
situated  behind  the  point  in  which  the  prolongations  of  these  canals 
appear  to  meet  each  other.  Consequently  it  has  such  a  position  and 
shape  that  in  M.  rapheidolabis  it  would  seem  to  correspond  to  the 
presumed  line  of  pit  organs  behind  the  cross  commissural  canal  and 
not  to  this  canal,  and  it  thus  appears  to  really  represent  the  true  supra- 
temporal  commissure  of  fishes.  If  this  opinion  is  true,  the  homologue 
of  the  commissural  canal  of  M.  rapheidolabis  would  either  be  entirely 
lacking  or  be  represented  by  a  paired  line  of  pit  organs  corresponding 
to  the  posterior  head  line  of  pit  organs  in  recent  fishes.  (Cf.  Allis 
1889,  pp.  505-506;  1903,  p.  187;  1905;  1923,  pp.  195-201;  Herrick 
1901,  pp.  222-223;  Stensio  1921,  pp.  218,  263;  1922,  p.  192;  1923, 
p.  1258;  1925;  etc.) 


160    Field  Museum  of  Natural  History — Geology,  Vol.  IV. 

The  most  anterior  portion  of  the  cephalic  division  of  the  lateral  line 
situated  between  the  supratemporal  commissure  and  the  infraorbital 
canal,  does  not  open  outward  and  has  no  tubuli  at  all.  The  remaining 
portion,  on  the  contrary,  is  provided  with  numerous  short  tubuli,  which 
issue  on  the  lateral  side  and  in  ^lateral  direction  (PI.  XXX,  fig.  i). 
The  supratemporal  commissure'  also  has  numerous  tubuli,  but  these 
seem,  as  a  rule,  to  perforate  the  bones  in  a  straight  upward  direction 
(PI.  XXX,  fig.  i). 

Whether  there  was  a  preopercular  canal  or  not,  it  is  at  present 
impossible  to  decide. 

Remarks 

As  is  obvious  from  this  description,  the  form  described  here  as 
Epipetalichthys  wildungensis  is  well  separated  from  other  Macropeta- 
lichthyids  known  hitherto,  and  the  erection  for  it  of  a  new  genus  and 
species  is  therefore  fully  justified. 

SOME  GENERAL  REMARKS   ON  THE 
MACROPETALICHTHYIDS 

With  the  facts  previously  known,  it  has  not  been  possible  to  arrive 
at  any  certain  conclusion  concerning  the  relationships  of  the  Macropet- 
alichthyids,  but  from  what  has  now  been  determined  some  deductions 
may  be  made.  Thus,  there  cannot  be  the  slightest  doubt  that  the 
Macropetalichthyids  are  true  fishes,  and,  moreover,  it  is  also  clear  that 
among  recent  forms  they  most  resemble  the  Elasmobranchs.  The 
most  important  characters  which  they  have  in  common  with  these 
are  the  following:  (i)  The  general  shape  of  the  primordial  neuro- 
cranium,  especially  the  tendency  to  broadening  of  the  ventral  surface, 
partly  at  the  expense  of  the  lateral  surfaces.  (This  is  especially  the 
case  in  the  labyrinth  region  in  which  the  sacculus  and  perhaps  the 
canalis  semicircularis  externus  had  about  the  same  relation  to  the 
ventral  surface  as  in  Chlamydoselachus  and  most  other  Selachians). 
(2)  The  position  and  relations  of  the  olfactory  capsule.  (3)  The 
presence  of  a  nasal  fontanelle  on  the  lower  side  of  the  nasal  capsule 
as  in  Chlamydoselachus  and  certain  other  Selachians.  (4)  The  pres- 
ence of  the  cavum  precerebrale.  (5)  The  general  shape  of  the  laby- 
rinth, especially  with  regard  to  the  position  of  certain  of  its  main  parts, 
as,  for  instance,  the  utriculus.  (6)  The  presence  of  the  ductus  endo- 
lymphaticus  and  the  fact  that  there  probably  was  a  distinct  fossa 
endolymphatica  on  the  dorsal  surface  of  the  primordial  neurocranium 
beneath  the  dermal  bones.     (7)  The  fact  that  the  ductus  endolympha- 


Macropetalichthyids  and  other  Arthrodires — Stensio     161 

ticus  perforated  the  dermal  cranial  roof  and  had  an  external  opening 
situated  as  in  certain  primitive  Selachians  (Chlamydoselachus).  (8) 
The  general  shape  of  the  brain  as  far  as  this  can  be  restored  from  the 
exit  of  the  nerve  canals  and  the  shape  of  the  cavum  cerebrale.  (9)  To 
a  certain  extent  the  course  and  arrangement  of  the  blood-vessels  and  the 
presence  of  certain  important  trunks,  as,  for  instance,  the  vena  hyoidea. 
(10)  The  fact  that  the  palatoquadrates  as  far  as  can  be  judged  did  not 
articulate  with  the  ethmoidal  region  but  must  have  been  suspended  be- 
low this  by  ligaments.  (11)  The  probable  course  of  the  anterior  part 
of  the  supraorbital  sensory  canal.  (It  should  also  be  mentioned  that 
the  sensory  canals  must  have  had  rather  numerous  sense  organs  and 
that  they  opened  outward  with  very  many  tubuli.) 

There  are,  of  course,  many  differences  between  the  Macropetalich- 
thyids and  Elasmobranchs,  but  these  differences  seem  in  general  from 
the  morphological  point  of  view  to  be  of  much  less  importance  than 
the  agreements.  The  fact  that  bone  occurs  to  a  considerable  extent  in 
the  Macropetalichthyids,  while  it  is,  as  we  know,  totally  lacking  in 
recent  Elasmobranchs,  ought  at  first  perhaps  to  be  considered  as  an 
important  difference,  but  from  what  is  now  known  of  the  occurrence 
of  bone  in  the  vertebrate  series,  even  this  must  be  considered  to  be 
a  character  of  minor  importance.  In  order  to  illustrate  this  the  fol- 
lowing facts  are  given : 

Typical  bone  tissue  is  found  in  the  Cephalaspids,  which,  according 
to  my  recent  investigations  not  yet  published,  are  lowly  organized 
vertebrates,  without  jaws,  with  three  distinct  prootic  branchiomeres 
(hyoid  segment,  mandibular  segment,  and  premandibular  segment)  and 
indications  of  still  more.  Further,  there  are  in  them  also  certain  evi- 
dences that  there  were  two  segmentally  arranged  nerves  anterior  to  the 
facialis,  and  we  are  able  to  conclude  that  they  were  in  these  respects 
much  more  primitive  even  than  the  recent  Cyclostomes.  As,  in  addition, 
more  or  less  osteoid  tissues  occurs  in  a  number  of  other  very  lowly 
organized  Ostracoderms,  we  conclude  that  bone  must  be  a  tissue 
that  appeared  very  early  and  very  low  down  among  the  vertebrates, 
in  fact  already  in  the  common  stem  of  fishes  and  Cyclostomes. 
It  is  also  well  worthy  of  notice  in  this  connection  that  in  the  Cephala- 
spids both  the  brain  and  the  ears  were  situated  in  the  bone  of  the 
cephalic  shield,  which  means  that  there  is  in  them  no  difference  be- 
tween dermal  bone  and  substitution  bone. 

In  the  earliest  appearing  Dipnoans,  Crossopterygians  and  Actin- 
opterygians  the  primordial  neurocranium  and  primordial  skeleton  in 
general  are  regularly  well  ossified,  but  the  degree  of  ossification  grad- 


1 62     Field  Museum  of  Natural  History — Geology,  Vol.  IV. 

ually  decreases  during  the  course  of  the  geological  periods,  the  sub- 
stitution bone  in  many  forms  being  finally  entirely  lost.  We  thus 
find  that  the  primordial  neurocranium  in  the  Devonian  Dipnoi 
Scaumenacia  (my  own  observations)  and  Dipterus  (Traquair  1878, 
p.  5;  Watson  and  Day  1916,  p.  33;  observations  made  by  the  author 
in  the  Royal  Scottish  Museum, 'Edinburgh)  is  very  well  ossified,  while 
it  is  not  found  to  be  ossified  in  any  of  the  Carboniferous  or  post- 
Carboniferous  forms,  if  we  except  the  small  ossification  in  the 
most  posterior  part  of  the  occipital  region  of  the  recent  Ceratodus  (Cf. 
Watson  and  Gill  1923 ;  K.  Furbringer  1904,  PI.  38,  fig.  7 ;  Teller 
1891 ;  etc.).  Among  the  Crossopterygians  the  process  of  reduction 
of  the  bone  tissue  is  especially  well  displayed  in  the  Coelacanthida,  in 
which  the  Devonian  form  Diplocercidcs  has  the  primordial  neurocran- 
ium comparatively  well  ossified  (Stensio  1922;  1923,  pp.  1259-1269), 
while  the  post-Devonian  forms  all  have  it  to  a  very  considerable  extent 
consisting  of  cartilage,  the  bone  being  limited  only  to  certain  spots 
(Stensio  1921,  pp.  53-61,  91-94,  120-122;  Watson  1921 ;  cf.  also 
Stensio  1923,  pp.  1241-1259).  According  to  information  which  I 
have  received  from  Professor  D.  M.  S.  Watson  of  London,  the  pri- 
mordial neurocranium  is,  further,  much  more  ossified  in  the  Carbonifer- 
ous Palseoniscids  than  in  the  Triassic  ones  Birgeria  and  Acrorhabdus 
(Stensio  1921,  pp.  152-175,  182-186,  187-198,  211,  224,  etc.;  pp.  238- 
250).  Similar  conditions  are  also  met  with  in  the  Saurichthyids,  in 
which  those  from  the  lower  Triassic  have  their  primordial  skeleton 
very  completely  ossified,  while  primordial  bone  seems  to  be  almost  en- 
tirely lacking  in  those  from  the  lower  Jurassic  (Stensio  1925).  In 
the  Chondrosteids,  Acipenserids  and  Polyodontids,  which  are  very 
closely  related  to  the  Palaeoniscids  and  Saurichthyids,  the  primordial 
neurocranium,  as  we  know,  is,  as  a  rule,  without  bone.  (We  find 
bones  only  in  very  old  specimens  which  indicates  that  the  bone  has 
lost  its  importance  and  that  the  parts  still  remaining  therefore  develop 
onto-genetically  very  late.)  Finally,  in  a  newly  discovered  ganoid 
from  China,  which  with  regard  to  its  cranial  anatomy  much  resembles 
Amia,  the  primordial  skeleton  is  much  more  ossified  than  in  Anna. 

A  similar  reduction  affects  in  several  forms  also  the  dermal  bones. 
In  the  Dipnoi  from  the  Devonian  the  dermal  bones  all  lie  superficially, 
are  ganoine-covered  and  well  developed  (Cf.  Watson  and  Gill  1923). 
In  many  post-Devonian  Palaeozoic  Dipnoans  on  the  contrary,  we  see 
that,  for  instance,  the  most  anterior  and  posterior  bones  of  the  dermal 
cranial  roof  sink  down  beneath  the  surface  of  the  dermis,  lose  their 
ganoine  covering  and  the  grooves  for  head  lines  of  pit  organs,  and,  in 


Macropetalichthyids  and  other  Arthrodires — StensiS     163 

the  recent  Ceratodus,  this  procedure  has  gone  so  far  that  the  anterior 
and  posterior  parts  of  the  dorsal  side  of  the  primordial  neurocranium 
are  uncovered  by  dermal  bones  (Cf.  Teller  1891,  Figs.  2-4;  cf.  also 
K.  Furbringer  1904,  pp.  498-500,  who  strangely  enough  arrives  at  a 
quite  opposite  conclusion).  The  same  procedure  as  the  one  described 
in  the  Dipnoi  has  taken  place  in  several  other  Teleostomes,  as,  for  in- 
stance, in  the  Chondrosteids,  the  Acipenserids  and  Polyodontids,  which 
all  are  certainly  descendants  from  forms  with  a  very  completely  de- 
veloped dermal  skeleton. 

From  the  facts  now  given  we  thus  find  that  most  groups  of  Tele- 
ostomous  fishes  in  which  the  skeleton  has  been  investigated  in  detail, 
undoubtedly  appear  to  be  degenerating  with  regard  to  the  degree  of 
ossification.  And  in  this  connection  it  is  worthy  of  notice  that  the 
Macropetalichthyids  themselves  too  seem  to  represent  a  degenerative 
series  in  this  respect,  as  the  primordial  neurocranium  of  the  middle 
Devonian  Macropetalichthys  rapheidolabis  is  much  more  completely 
ossified  than  that  of  the  upper  Devonian  Epipetalichthys  wildungensis. 

If  we  turn  to  the  Elasmobranchs,  it  has  generally  been  considered 
that  these  do  not  have  real  bone  tissue.  This  may  be  true  for  the 
more  typical  later  forms,  but  if  we  go  back  to  the  Acanthodians  the 
conditions  seem  to  be  different.  Reis  (1896,  pp.  179-184,  PI.  VII, 
fig.  1)  and  with  him  most  other  authors  certainly  say  that  in  these  too 
there  is  no  bone,  but  that  the  primordial  skeleton  is  calcified.  But,  as 
is  evident  from  Reis'  description  and  figures,  the  manner  of  "calcifica- 
tion" is  there  of  quite  another  kind  from  that  in  the  typical  Elasmo- 
branchs and  in  reality  everything  indicates  that  in  the  so-called  calcified 
cartilage  of  Acanthodians  we  are  concerned  with  true  bone.  That 
Reis1  did  not  recognise  it  as  bone  is  probably  due  simply  to  the  fact 
that  he  expected  to  find  the  bones  of  fishes  with  the  structure  occurring 
in  higher  vertebrates,  i.e.,  throughout,  or  almost  throughout,  with  a 
lamellary  structure  and  the  lamellae  in  the  interior  of  the  skeletal  ele- 
ments surrounding  Haversian  canals.  This,  however,  is  often  not 
the  case,  the  bone  of  lower  vertebrates  generally  being  entirely  without 
Haversian  canals  and  lamellae  and  even  rather  often  without  cells. 
Unfortunately  the  knowledge  of  the  microscopic  structure  of  bone  in 

'According  to  Reis  the  primordial  skeleton  of  the  Acanthodes  consists  peripher- 
ally of  a  rather  lamellary  layer  containing  numerous  cell  spaces.  Internally  to 
this  follows  a  cancellous  layer  and  most  centrally  a  vacuity  occupied  in  the  fossil 
by  stone  but  which  in  the  living  animal  certainly  consisted  of  cartilage.  In  the 
cancellous  layer  there  are,  if  Reis  is  correct,  no  cell  spaces.  A  microscopic  inves- 
tigation of  the  primordial  skeleton  of  the  Acanthodians,  from  the  new  points  of 
view  advanced  here  would  be  very  desirable,  but  unfortunately  I  had  no  mate- 
rial with  which  to  undertake  one  myself. 


1 64    Field  Museum  of  Natural  History — Geology,  Vol.  IV. 

lower  vertebrates  is  still  very  imperfect.  The  conditions  in  several 
other  Elasmobranchs  from  the  Palaeozoic  also  seem  to  indicate  that 
the  Elasmobranchs  in  general  originally  had  an  osseous  skeleton  (Cf. 
Woodward  1924).  Finally,  it  ought,  in  connection  with  this  also,  to 
be  pointed  out  that,  according  to  the  recent  interesting  investigations  by 
Weiden reich  (1923,  pp.  4 1 5-4I 9,  461-462),  there  is  really  no  funda- 
mental difference   between   calcification   and   ossification. 

From  what  we  now  know  of  the  occurrence  of  bone  in  the  vertebrate 
series,  we  must  evidently  presume  that  bone  must  have  occurred  also 
in  the  ancestors  of  and  in  the  most  primitive  Elasmobranchs  and  the 
fact  that  it  is  to  be  found  in  the  Acanthodes  is  therefore  only  a  matter 
of  course. 

That  the  Macropetalichthyids  cannot  be  closely  related  to  any 
Teleostomous  fishes  so  far  known  is  thus,  despite  the  presence  of  bone 
in  their  skeleton,  beyond  question.  The  development  of  the  dermal 
bones  in  their  cranial  roof  and  the  lacking  of  dermal  bones  on  the 
ventral  side  of  the  primordial  neurocranium,  together  with  the  Elasmo- 
branchian  characters,  show  definitely  that  they  are  not  specialized 
Teleostomes  at  all  but  forms  that  among  fishes  known  hitherto  are  in 
some  way  most  closely  related  to  the  Elasmobranchs.  In  fact  the  indi- 
cations as  far  as  we  can  judge  at  present  seem  to  be  that  the  Macro- 
petalichthyids evolved  from  some  early,  very  primitive  Elasmobranchian 
form  soon  after  the  Elasmobranchian  stem  had  separated  from  the 
stem  of  Teleostomous  fishes. 

CERTAIN  REMARKS  CONCERNING  THE  OTHER  NON- 
MACROPETALICHTHYID   ARTHRODIRES 

The  increased  knowledge  that  we  now  possess  of  the  anatomy  of 
the  Macropetalichthyids  throws  of  course  new  light  on  the  other 
Arthrodires  too,  and  it  is  therefore  of  importance  to  give  here  some 
remarks  on  these.  I  shall  begin  with  the  Phlyctenaspids,  which,  as 
Jaekel  has  pointed  out  (1911,  p.  46)  seem  to  be  most  nearly  related 
to  the  Macropetalichthyids.  I  shall  then  turn  to  the  Coccosteids, 
Homosteids,  Mylostomids,  Ptyctodontids  and,  finally,  to  a  form  which 
has  not  hitherto  been  recognized  as  an  Arthrodire.1 

1A  satisfactory  classification  of  the  Arthrodires  into  families  is  difficult  to 
give  at  present  on  account  of  the  imperfect  knowledge  we  still  possess  of  the 
various  forms,  and  because  the  opinions  of  different  authors  are  widely  at  vari- 
ance in  this  respect.  The  subdivisions  given  by  me  here  are  merely  intended  to 
simplify  the  account  of  certain  anatomical  features  and  not  to  give  positive 
conclusions  as  to  the  mutual  relations  of  all  the  forms. 


Macropetalichthyids  and  other  Arthrodires — Stensio     165 

THE  PHLYCTENASPIDS 

To  the  Phlyctenaspids  are  here  referred  among  others  the  genera 
Phlyctenaspis  and  Acanthaspis  (Arctolepis,  Eastman  1908  b;  Kaer 
1916). 

Primordial  Neurocranium 

Of  the  primordial  neurocranium  no  remains  have  been  found  so 
far,  a  fact  which  indicates  that  it  was  either  entirely  cartilaginous 
or  at  least  very  slightly  ossified.  Despite  this,  it  is,  however,  possible 
with  the  help  of  the  configuration  of  the  dermal  cranial  roof  and  the 
conditions  in  the  Macropetalichthyids,  to  obtain  an  idea  of  its  general 
shape,  at  least  in  the  anterior  parts.  (See  Fig.  20.)  It  is  thus  obvious 
that  the  ethmoidal  and  labyrinth  regions  must  both  have  been  very 
short  and  broad  and  that  the  labyrinth  region  was  rather  long,  in  any 
case  several  times  as  long  as  the  two  first-mentioned  regions.  It 
seems  probable  also  that  the  occipital  region  was  rather  long,  too.  The 
differences  with  regard  to  general  extent  of  the  various  regions  from 
those  in  Macropetalichthys  rapheidolabis  can  be  clearly  seen  by  com- 
paring Fig.  20  with  Figs.  1,  3,  5,  etc. 


Fig.  20.    Phlyctenaspis  acadica 

Restoration  of  the  outlines  of  the  primordial  neurocranium  with  the  guidance 
of  the  shape  of  the  dermal  cranial  roof  (Cf.  Fig.  21)  and  the  conditions  in 
Macropetalichthys  rapheidolabis.  Shape  of  the  cavum  cerebrale  indicated  by 
broken  lines.     X^- 

Olf,  olfactory  capsule;  orb,  orbit;  par,  pineal  opening. 


1 66    Field  Museum  of  Natural  History — Geology,  Vol.  IV. 

By  the  use  of  broken  lines  I  have  tried  in  Fig.  20  to  indicate 
the  possible  shape  and  extension  of  the  cavum  cerebrale  cranii,  which 
if  my  view  is  correct  ought  to  have  been  fairly  like  that  in  Macropet- 
alichthys  except  that  the  canals  for  the  tractus  olfactorii  must  have 
diverged  very  strongly  and  rapidly  from  each  other.  As  the  anterior 
median  dermal  bone  plate  M  (Fig.  21)  has  on  the  lower  side  close 
to  its  posterior  border  a  pronounced  pit  corresponding  to  the  pineal 
pit  in  Titanichthys,  we  are  quite  sure  of  the  position  of  the  dorsal 
part  of  the  canal  par,  and  from  this  we  are  of  course  able  to  conclude 
approximately  where  the  anterior  end  of  the  cavum  cerebrale  cranii 
was  situated.  Whether  there  was  any  distinct  cavum  precerebrale  or 
not  it  is  not  possible  to  decide,  and,  finally,  it  may  be  added  that  no 
external  opening  of  the  canal  for  the  ductus  endolymphaticus  has  hith- 
erto been  observed. 


Fig.  21.    Phlyctenaspis   acadica 

Dermal  cranial  roof.  Sensory  canal  grooves  with  dotted  outlines.  Ornament 
not  drawn.  Sketch  made  after  specimen  P.  6555  in  the  British  Museum,  Lon- 
don.    XVa- 

A,  B,  I,  L,  M,  Pi,  Pi,  S,  dermal  bones  of  the  cranial  roof  ifc,  infraor- 
bital sensory  groove  (blue)  ;  Ic,  cephalic  division  of  the  lateral  line  (red)  n, 
nasal  aperture;  orb,  orbital  entrance;  poc,  preopercular  sensory  groove  (yellow)  ; 
soc,  supraorbital  sensory  groove  (green),  t,  line  on  the  plate  M,  perhaps  a  vestigial 
suture. 


Macropetalichthyids  and  other  Arthrodires — Stensio     167 

Dermal  Cranial  Roof 

The  plates  Plt  P2,  and  S  (Fig.  21)  correspond,  at  least  in  the 
main,  to  the  plates  in  Macropetalichthyids  lettered  Plt  P2,  and  5" 
(Figs.  15,  19),  while  the  plate  /  certainly  represents  a  posterior  part 
of  the  plate  M2  of  the  latter.  The  plate  B  (Fig.  21)  seems  to 
include  the  homologues  of  the  plates  L2  and  L3,  in  the  Macropetalich- 
thyids, together  with  a  part  of  the  plate  M2  in  these.  The  plate  A 
(Fig.  21)  is,  as  far  as  can  be  seen  at  present,  represented  in  the 
Macropetalichthyids  by  the  plate  Lx,  and  an  anterior  part  of  the  plate 
M2.  The  plate  L  and  the  most  anterior  part  of  the  plate  M,  seem  to 
be  without  homologues  in  Macropetalichthyids  and  that  in  this  case 
we  are  concerned  with  reductions  in  the  last-mentioned  forms  is  highly 
probable  from  the  conditions  in  the  other  Arthrodires.  The  plate  M 
has  probably  arisen  by  the  coalescence  of  two  plates,  an  anterior  and  a 
posterior  one,  homologous  to  the  rostral  and  pineal  plates  respectively 
of  the  Coccosteids  (Fig.  24)  as  it  is  crossed  by  a  fine  transverse  line 
which  seems  to  be  the  vestigial  suture  between  the  presumed  two  com- 
ponents. 

As  far  as  can  be  judged  at  present  from  the  different  conditions  of 
their  dermal  cranial  roofs,  the  Macropetalichthyids  and  Phlyctenaspids 
must  both  have  descended  from  primitive  Arthrodires  in  which  the 
medial  parts  of  the  cranial  roof  were  occupied  by  a  larger  number  of 
bone  plates  than  in  any  Arthrodire  known  hitherto. 

Between  the  plates  L  and  Px  there  is  in  the  fish  a  rounded  notch 
(orb,  Fig.  21)  indicating  the  position  of  the  certainly  very  small 
orbital  entrance,  which  is  thus  in  relation  to  the  dermal  cranial  roof 
situated  in  another  manner  than  in  the  Macropetalichthyids  and  which 
in  addition  appears  to  be  directed  much  more  laterally  than  in  these. 
Concerning  the  ventral  boundaries  of  the  orbital  entrance  nothing 
certain  is  known  at  present.  Between  the  antero-medial  border  of 
the  plate  L  and  the  postero-lateral  border  of  the  plate  M,  there  is 
found  another  notch  in  the  outline  of  the  dermal  cranial  roof,  a  notch, 
which  as  far  as  I  can  see,  must  be  the  external  nasal  aperture  (n,  Fig. 
30. 

Most  of  the  dermal  bones  are  ornamented  with  tubercles  and  must 
have  had  a  superficial  position.  Only  the  most  anterior  bones  L  and 
M  seem  to  have  been  situated  somewhat  deeper  in  the  skin,  as  at 
least  their  anterior  parts  usually  seem  to  be  without  ornament  and  the 
supraorbital  sensory  canal  anterior  of  the  plate  A  probably  passed 
entirely  externally  of  the  plate  L. 


1 68    Field  Museum  of  Natural  History — Geology,  Vol.  IV. 

Sensory  Canal  System  of  the  Head 

The  sensory  canals  are  known  only  on  the  dermal  cranial  roof, 
on  which  they  form  open  grooves.  These  grooves  are,  however,  at 
least  in  several  cases,  deep  and  narrower  at  their  external  opening 
than  further  inwards  (Fig.  22V  so  that  they  in  fact  open  outwards 
only  with  a  narrow  slit.  Concerning  the  number  of  sense  organs 
in  the  grooves  nothing  can  be  said  at  present. 

The  supraorbital  groove  (soc,  Fig.  21),  which  is  very  short, 
has  its  posterior  end  at  about  the  ossification  centre  of  the  plate  A. 
From  this  point  it  passes  forward  and  laterally  to  the  antero-lateral 
corner  of  the  plate.  On  the  plate  L,  there  are  no  traces  of  it,  but 
it  certainly  continued  still  further  forwards,  although  situated  there 
entirely  externally  of  the  plate  L  in  the  most  external  layers  of  the 
skin.  From  the  direction  of  the  part  known  of  the  groove  it  seems, 
as  is  obvious  from  text  fig.  21,  certain  that  the  other  hitherto  unknown 
part  of  the  same  groove  passed,  as  has  already  been  emphasized  above, 
antero-latero-ventrally  posterior  of  the  nasal  aperture  as  it  does  in  the 
Coccosteids  and  Elasmobranchs. 


Fig.  22.  Sketch  of  a  sensory  canal  groove  of  a  Phlyctenaspid  in  transversal 
section.     Magnified. 

The  infraorbital  groove  (ifc,  Fig.  21)  is,  with  its  posterior 
end,  which  is  situated  approximately  at  the  ossification  centre  of  the 
plate  P2,  continuous  with  the  cephalic  portion  of  the  lateral  line  groove. 
It  goes  forward  to  about  the  ossification  center  of  the  plate  Plt  where 
it  suddenly  bends  latero-ventrally  and  leaves  the  cranial  roof  posterior 
to  the  orbital  entrance. 

Just  at  the  bend,  it  is  continuous  with  a  groove  (ifbr,  Fig.  21) 
which  goes  in  an  arch  postero-medially  to  near  the  centre  of  the  plate 
B.  This  groove  must,  as  is  easily  understood,  have  been  innervated 
either  from  the  n.  ophthalmicus  lateralis  and  represent  a  posterior 
part  of  the  supraorbital  sensory  canal,  or  from  the  r.oticus  lateralis, 
in  which  case  it  must  be  considered  as  a  branch  from  the  infraorbital 
groove.  Which  one  of  these  two  alternatives  is  the  true  one  it  is 
difficult  to  decide  from  the  conditions  in  the  Phlyctenaspids,  but  when 
we  come  to  the  Coccosteids  we  find  there,  as  we  shall  see,  certain  facts 
which  seem  to  be  much  in  favour  of  the  latter.  I  have  therefore 
called  the  groove  in  question  the  postero-medial  branch  of   the  in- 


Macropetalichthyids  and  other  Arthrodires — Stensio     169 

fraorbital  groove.  A  further  support  for  this  view  is  given  perhaps 
by  the  conditions  in  Lcemargus.  In  this  form  the  infraorbital  canal 
with  its  posterior  part  on  the  dorsal  side  of  the  head,  turns  abruptly 
medially  and  continues  in  this  direction  till  it  almost  meets  its  fellow 
of  the  opposite  side  in  the  median  line  (Ewart  1892,  PI.  I,  fig.  1). 

A  groove  issuing  in  postero-medial  direction  from  the  in- 
fraorbital groove  quite  in  the  same  manner  as  the  postero-medial 
branch  of  the  infraorbital  groove  in  the  Phlyctenaspids  occurs  in  many 
Stegocephalians  (Wiman  1914,  PI.  I,  figs.  1,  2,  3;  PI.  Ill,  fig.  2;  PI. 
IV,  figs.  2,  6,  7;  PL.  V,  fig.  I;  PI.  VII,  in  the  form  figured  on  this 
plate  the  branch  in  question  is  double;  1916,  PI.  XV,  cf.  Moodie  1908; 
1915).  A  homologue  to  it  is  also  found  in  larval  forms  of  Triton, 
in  which,  however,  like  the  whole  sensory  canal  system,  it  is  repre- 
sented merely  by  isolated  pits  arranged  in  a  line. 

The  cephalic  division  of  the  lateral  line  (Ic,  Fig.  21)  is,  as 
already  pointed  out,  like  the  other  sensory  canals,  an  open  groove. 
Its  anterior  end  is  situated  as  the  ossification  centre  of  the  plate  P2, 
in  which  it  is  continuous  with  the  infraorbital  groove.  It  goes  back- 
ward to  the  postero-lateral  edge  of  the  plate  S,  its  farther  course  back- 
ward being  unknown.  There  is  no  cross  commissural  groove,  which 
connects  it  with  its  fellow  of  the  opposite  side  and,  as  far  as  known, 
there  is  not  even  any  pit  line  representing  a  commissure  of  this  kind. 

The  preopercular  groove  (poc,  Fig.  21)  is  represented  by  a 
dorsal  part  which  issues  in  a  postero-latero-ventral  direction  from  the 
point  at  which  the  infraorbital  groove  and  the  lateral  line  groove  (Ic) 
meet  one  another. 

Nothing  is  known  of  pit  lines,  but  this  may  perhaps  be  due  to  the 
unfavorable  state  of  preservation  in  which  remains  of  Phlyctenaspids 
are  generally  found. 

Dermal  Covering  of  the  Trunk 

The  anterior  parts  of  the  trunk  of  the  Phlyctenaspids  are,  as  we 
know,  enclosed  in  a  strong  armour,  which,  as  it  follows  immediately 
behind  the  head,  obviously,  at  least  with  its  anterior  parts,  occupies 
the  position  of  the  dermal  shoulder  girdle  of  the  TeleostomoUs  fishes. 
A  further  support  for  this  view  is  the  fact  that,  as  set  forth  in  the 
description  of  M.  raphcidolabis,  the  branchial  basket  cannot  have  ex- 
tended backward  into  the  abdominal  armour,  but  must  have  been 
limited  entirely  to  the  head.  The  powerful  Elasmobranchian-like  spine 
that  in  all  Phlyctenaspids  is  rigidly  attached  to  the  antero-lateral  edge 
of  the  antero-ventro-lateral  and  the  lateral  edge  of  the  inter-lateral 


170    Field  Museum  of  Natural  History — Geology,  Vol.  IV. 

of  each  side,  thus  has  in  fact  the  approximate  position  of  the  pectoral 
fin  of  ordinary  fishes  and  seems  to  me  to  represent  either  the  entire 
dermal  skeleton  of  this  fin  or  to  be  a  spine  that  was  attached  to  its 
anterior  border  while  the  other  parts  of  the  fin  have  become  reduced. 

THE^TOCCOSTEIDS 

To  the  Coccosteids  in  the  broad  sense  in  which  they  are  taken 
here  are  referred  not  only  Coccostens,  Pachyosteus,  Rhinosteus,  Pholi- 
dosteus,  Chelyophorus,  and  others,  but  also  such  genera  as  Dinichthys, 
Titanichthys,  and  Selenosteus,  the  chief  reason  for  this  being  the 
characters  of  their  dermal  cranial  roof. 

Primordial  Neurocranium 

In  Chelonichthys  primigenius  (Eichwald  i860,  pp.  1526-1527  PI. 
57,  figs.  1,  2)  the  primordial  neurocranium  was  partly  well  ossified, 
but  unfortunately  no  details  are  known  of  it.  In  other  forms  it  seems 
as  a  rule  to  have  been  entirely  cartilaginous  or  at  least  almost  entirely 
so,  for  no  certain  remains  of  it  have  been  found  so  far. 

Turning  first  to  Coccosteus  decipiens  and  the  forms  closely  allied 
to  it,  we  can  at  once  understand  from  the  proportions  of  the  dermal 
cranial  roof  that  the  ethmoidal  and  occipital  regions  of  the  primordial 
neurocranium  in  them  must  have  been  short,  while  the  remaining  two 
regions,  the  orbitotemporal  and  labyrinth  regions,  had  a  rather  con- 
siderable length.  It  deserves  also  to  be  mentioned  in  this  connection 
that  the  primordial  neurocranium  must  have  been  fairly  high,  in  any 
case  higher  than  in  the  dorso-ventrally  much  flattened  Macropetalich- 
thys  rapheidolabis.  That  this  was  the  case  is  easily  understood  if  we 
look  at  the  head,  for  instance,  of  Pholidosteus  friedelii  (Jaekel  1919, 
Fig.  2)  from  the  lateral  side.  In  Fig.  23  A,  the  general  shape  of 
the  primordial  neurocranium  has  been  drawn  as  I  suppose  it  to  have 
appeared.  In  this  figure  also  the  outlines  of  the  cavum  cerebrale 
cranii  and  the  canals  for  the  olfactory  tracts  have  been  put  in  mainly 
with  the  guidance  of  the  conditions  in  M.  rapheidolabis  and  the  posi- 
tions of  the  nostrils  and  the  pineal  pit  on  the  lower  side  of  the  pineal 
plate  {Pi,  Fig.  24).  We  see  from  this  that  the  canals  for  the  ol- 
factory tracts  cannot  have  diverged  quite  so  strongly  forward  as  in  the 
Phlyctenaspids. 

While  in  Coccosteus  and  its  nearest  allies  the  lower  side  of  the 
dermal  cranial  roof  is  rather  smooth,  or  in  any  case  without  prominent 
ridges  or  formations  of  this  kind,  it  has  in  Dinichthys  a  paired  lamella, 
which  extends  some  distance  downwards.    The  position  of  this  lamella, 


Macropetalichthyids  and  other  Arthrodires — Stensio     171 

which  in  places  is  thickened  or  is  provided  with  downward  di- 
rected processes  or  is  irregular  in  other  ways,  is  shown  by  Fig.  2, 
PI.  IV,  and  Fig.  1,  PI.  LII  of  Newberry's  description  in  1889,  and  by 
Fig.  4  D  of  Woodward's  description  in  1922,  and,  as  we  understand 
from  these  figures,  it  must  have  covered  a  dorsal  portion  of  the  outer 
surface  of  each  lateral  wall  of  the  primordial  neurocranium.  Accord- 
ingly it  shows  the  outlines  of  the  dorsal  side  of  the  primordial  neuro- 
cranium, a  fact  that  was  recently  pointed  out  by  Woodward  (1922, 

P- 33). 

With  the  guidance  of  this  lamella  and  the  conditions  in  the 
Macropetalichthyids,  the  restoration  shown  in  Fig.  23  B  was  made. 
As  we  see  from  it,  the  primordial  neurocranium  of  Dinichthys  agrees 
in  several  points  with  that  in  the  Phlyctenaspids  and  Coccosteus  but 


Fig.  23.  Restoration  of  the  outlines  of  the  primordial  neurocranium.  A,  of 
Coccosteus;  B,  of  Dinichthys.  The  possible  extension  of  the  cavum  cerebrale 
cranii  and  the  olfactory  tracts  is  indicated  by  broken  lines,  co,  occipital  condyles ; 
olf,  olfactory  capsule;  orb,  orbit. 

differs,  however,  distinctly  at  least  from  that  in  the  former  by  the 
greater  length  and  comparatively  less  considerable  breadth  of  its  orbi- 
totemporal region.  Further,  it  is  also  worthy  of  notice  that  the  orbito- 
temporal region  probably  was  not  definitely  bounded  from  the  labyrinth 
region,  but  that  the  anterior  parts  of  this  were  rather  narrow  too,  while 
its  posterior  parts  were  very  broad.  Whether  the  short  occipital  region 
had  an  anterior  broad  division  as  in  the  Macropetalichthyids  it  is  riot 
possible  to  say,  as  we  do  not  know  how  the  vagus  canal  had  its  course. 
According  to  the  opinion  advanced  by  Woodward  (1922,  p.  33) 
the  primordial  neurocranium  in  Dinichthys  would  not  have  extended 
farther  back  beneath  the  dermal  cranial  roof  than  approximately  to 


172     Field  Museum  of  Natural  History — Geology,  Vol.  IV. 

the  transversal  plane  through  the  posterior  ends  of  the  supraorbital 
sensory  canals  (cf.  Fig.  24  B).  In  the  Macropetalichthyids  the 
posterior  ends  of  the  supraorbital  canals  are,  as  is  seen  from  PI.  XX  in 
the  present  paper  situated  at  a  place  about  midway  between  the  laby- 
rinth cavities.  In  other  fishes,  too, '  they  do  not  reach  much  farther 
back,  even  in  those  cases  whenuiey  with  certainty  include  the  anterior 
head  lines  of  pit  organs.  This  fact  in  connection  with  the  circum- 
stance that  the  paired  lamella  on  the  lower  side  of  the  dermal  cranial 
roof  distinctly  continues  postero-laterally  of  this  place  to  the  very 
postero-lateral  corner  of  the  dermal  cranial  roof,  seems  to  me  to  indi- 
cate with  almost  absolute  certainty  that  the  primordial  neurocranium 
of  Dinichthys  extended  backward  as  far  as  the  dermal  cranial  roof 
and  that  the  posterior  parts  of  the  labyrinth  region  were  as  broad  as 
shown  by  my  restoration  in  Fig  23  B. 

The  paired  bony  lamella  on  the  lower  side  of  the  dermal  cranial 
roof  in  Dinichthys  is  held  by  Woodward  to  be  an  ossified  dorso- 
lateral part  of  the  lateral  wall  of  the  primordial  neurocranium  and  we 
would  thus  have  here  a  primordial  component  coalesced  with  the  der- 
mal cranial  roof.  That  this  perhaps  is  the  case  seems  probable  to  me 
especially  from  the  conditions  in  the  Coelacanthids,  in  which  a  part  of 
the  primordial  skeleton  in  certain  specialized  Triassic  forms  has 
coalesced  with  an  overlying  dermal  bone,  while  in  the  other  forms  it 
has  retained  its  original  primitive  relations  (Stensio  1921,  pp.  53,  93, 
97,  124;  1923,  p.  1269;  cf.  Allis  1899;  1909a).  In  the  Coelacanthids 
this  coalescence  between  dermal  bone  and  primordial  bone  has,  how- 
ever, obviously  taken  place  in  connection  with  a  process  of  reduction 
of  the  bone  of  the  primordial  neurocranium,  and,  from  what  has  been 
emphasized  above  there  is  every  reason  to  believe  that  this  is  also  the 
case  in  Dinichthys.  What  the  paired  bone  is  that  Newberry  (1889, 
pp.  147-148)  describes  from  the  interior  of  the  head  in  Dinichthys 
tcrelly,  it  is  not  possible  to  decide.  Perhaps  it  may  be  an  ossified  part 
of  the  primordial  neurocranium. 

A  common  character  for  all  the  Coccosteids  is  the  fact  that  their 
orbit  usually  was  large  and  that  the  eyes  must  have  been  directed 
straight  or  almost  straight  laterally. 

Dermal  Cranial  Roof 

The  dermal  cranial  roof  of  Coccosteus  decipiens  (Fig.  24  A;  25) 
is  rather  similar  to  that  in  Phylyctenaspis  (Fig.  21),  but  differs  from 
this  by  the  somewhat  different  shape  of  the  various  bones  and  the  fact 
that  the  rostral  plate  (R)  and  the  pineal  plate  (Pi)  are  always  inde- 


Macropetalichthyids  and  other  Arthrodires — Stensio     173 

pendent.  Further,  it  is  also  to  be  noticed  that  the  orbital  entrance  is 
bounded  dorsally  by  the  plate  A,  while  in  Phlyctenaspis  it  is  bounded 
there  by  the  plates  L  and  Plf  the  plate  A  there  lying  medially  of  the 
two  just-mentioned  plates.  The  external  nasal  aperture  is  paired,  sit- 
uated rather  close  to  its  fellow  of  the  opposite  side  and  directed  almost 
straight  forward.  It  is  bounded  medially  by  the  rostral  plate  (R), 
laterally  by  the  plate  L. 

The  upper  Devonian  Coccosteids  are  generally  more  specialized 
than  Coccostcus  decipiens.  (Cf.  Jaekel  1906a;  1907;  Dean  1901, 
figs.  14-18;  Eastman  1908a,  pp.  89-156;  1908b,  pp.  152-205; 
Bryant  1918,  pp.  26-105;  Woodward  1922,  fig.  4,  pp.  30-36.) 
The  ornament  of  the  bones  in  them  is  generally  fine  or  is  even  in  certain 
cases  lacking;  the  bones  have  become  firmly  united  to  one  another  and 
in  the  American  forms,  as,  for  instance,  Dinichthys ,  Titanichthys  and 
Stcnostens,  the  plate  L  has  hitherto  not  been  found.  This  indicates 
either  that  it  had  sunk  deep  down  in  the  skin  and  lost  its  connections 
with  the  neighbouring  plates  or  that  it  had  become  entirely  reduced,  as 
in  the  Macropetalichthyids  (Cf.  Woodward  1922,  p.  35). 

In  the  restorations  of  the  Dinichthy  s-species  exhibited  in  various 
American  museums,  no  consideration  seems  to  have  been  given  either 
to  the  absence  of  the  paired  plate  L  or  to  the  circumstance  that  the 
primordial  neurocranium  with  the  olfactory  capsules  must  have  ex- 
tended somewhat  forward  beyond  the  anterior  margin  of  the  plates  A 
(Fig.  24  B)  of  the  dermal  cranial  roof.  (Cf.  the  restoration  of  Dean 
1909,  Pis.  38-39;  and  by  Bryant  1918,  PI.  1,  both  of  which  are 
incorrect  in  this  respect.) 

Dermal  Bones  of  the  Cheek 

In  Coccosteus  decipiens  and  its  nearest  allies,  the  cheek  is  regularly 
occupied  by  two  bones,  a  large,  anterior  infraorbital  (So,  Fig.  24), 
which  forms  the  ventral  boundary  of  the  orbital  entrance  and  a  small 
plate  (Ps,  Figs.  24,  25) \  which  is  situated  behind  the  infraorbital  and 
occupies  the  most  posterior  part  of  the  cheek.  (Cf.  Traquair  1890, 
PI.  10,  figs.  1,  2;  Jaekel  1902,  Fig.  on  p.  107;  1919,  Fig.  2,  Qj.)  In 
the  American  forms  from  the  upper  Devonian  the  last  mentioned  plate 
is,  as  far  as  I  know,  always  lacking,  a  fact  which  probably  indicates 
that  it  has  become  reduced.  (Cf.  Eastman  1908a,  Figs.  23,  24,  29; 
1908b,  Figs.  27,  31;  Hussakof  1906,  Figs.  iB,  12;  Dean  1909,  Fig. 
56,  Pis.  38-40,  etc.) 

xIn  certain  cases  this  plate  may  probably  be  subdivided  into  two  (Jaekel  1902, 
Fig.  on  p.  107). 


174    Field  Museum  of  Natural  History — Geology,  Vol.  IV. 

Visceral  Skeleton 

The  primordial  visceral  skeleton  seems  generally  to  have  consisted 
chiefly  of  cartilage,  but  in  Pholidostcus  (Jaekel  1907,  pp.  176-186; 
1919,  pp.  77-87,  Figs.  4,  8)  and  Erromenosteus  (Jaekel  1919,  pp.  84- 
86,  Fig.  9)  it  is  certainly  at  least  partly  ossified. 

In  Dinichthys  intermedins  Woodward  has  found  a  bone  (Wood- 
ward 1922,  p.  35)  which  seems  to  belong  to  the  palatoquadrate,  but 
whether  this  bone  was  an  ossification  in  the  palotoquadrate  cartilage 
itself  or  whether  it  is  simply  a  dermal  bone  developed  in  relation  to  this, 
it  is  at  present  not  possible  to  decide.  The  occurrence  is,  however,  of 
much  interest,  because  it  shows  that  there  was  in  the  upper  jaw  of  the 
Arthrodires  a  palatoquadrate  medially  of  the  two  external  elements, 


xp 

Fig.  24a.    Dermal  cranial  roof 

A.    Coccostcus  decipiens   (sketch  drawn  by  the  author  from  specimens  in  the 
Royal  Scottish  Museum,  Edinburgh).    For  explanation  of  lettering  see  next  page. 

and  that  the  latter  two  elements  on  account  of  this  must  really  be  most 
nearly  comparable  with  the  premaxillary  and  maxillary  respectively. 
An  additional  support  for  this  interpretation  of  the  two  external  ele- 
ments in  the  upper  jaw  is'  the  fact  that  the  anterior  one  of  these  ele- 
ments in  certain  species  is  tuberculated  on  the  external  surface  (Wood- 
ward 1922,  p.  33;  Eastman  1908a,  PI.  7,  figs.  4-6)  and  accordingly 
appears  to  be  a  superficial  dermal  bone.  . 

The  Meckelian  cartilage  has  in  Pholidosteus  and  Erromenosteus 
(Jaekel  1907,  pp.  176-184;  1919,  Figs.  4,  8,  9)  its  pars  articularis 
ossified,  but  seems,  as  far  as  we  know,  generally  to  have  been  entirely 


Macropetalichthyids  and  other  Arthrodires — Stensio     175 

cartilaginous.1  On  the  medial  side  it  was  almost  entirely  covered  by 
the  large,  well-known  bone  (Mix,  Fig.  25)  which  has  been  termed  by 
various  authors  mandibular,  gnathal,  infero-gnathal,  dentary,  and 
splenial.  This  bone,  on  account  of  its  extent  and  relations,  obviously 
corresponds  to  all  the  dermal  bones  on  the  medial  side  of  the  man- 
dible in  the  Teleostomes  and  would  therefore  if  named  from  this 
point  of  view  get  a  very  complex  title.  For  the  sake  of  brevity  we 
may  call  it  simply  the  mixicoronoid  (Cf.  Stensio  1921,  p.  244).  On 
the  outside  of  the  postero-ventral  part  of  the  Meckelian  cartilage,  there 
is  in  Pholidostcus  (Jaekel  1907,  Fig.  5;  1919,  Fig.  4)  a  small  dermal 
bone  which  is  ornamented  with  tubercles  and  which,  as  pointed  out  by 


Ju* 


Fig.  24b.     Dermal  cranial  roof 

B.  Dinichthys  halmodeus  (Bones  after  Eastman  1908a,  Fig.  21,  and  1908b, 
Fig.  24).  Sensory  grooves  according  to  observations  made  by  the  author  on  a 
specimen  in  Albany,  N.  Y.     Much  diminished. 

Sensory  canal  grooves  in  both  A  and  B,  indicated  by  a  double  dotted  line 
and  colours. 

A,  B,  J,  L,  Pi,  Pi,  Pi,  R,  S,  bones  in  the  dermal  cranial  roof;  Ps,  So, 
bones  of  the  cheek;  ifc,  infraorbital  sensory  groove  (blue);  ifbr,  postero- 
medial branch  of  the  infraorbital  sensory  groove  (blue)  ;  juc,  jugal  groove 
(yellow)  ;  k,  lateral  line  groove  (red)  ;  tnp,  groove,  probably  for  the  middle 
head  line  of  pit  organs  (red);  na,  nasal  aperture;  orb,  orbital  entrance;  poc, 
preopercular  groove  (yellow)  ;  pp,  groove  probably  for  the  posterior  head  line 
of  pit  organs  (red)  :  soc,  supraorbital  groove  (green)  ;  xp,  branch  from  the 
cephalic  division  of  the  lateral  line  (groove),  probably  corresponding  to  a  part 
of  the  superatemporal  cross  commissure  (red). 

*I  have  had  the  opportunity  of  investigating  Pholidosteus  friedelii  in  the  col- 
lection of  Professor  O.  Jaekel  at  Greifswald  and  I  fully  agree  with  him  in  his 
interpretations  of  the  elements  in  the  lower  jaws  of  Arthrodires. 


176    Field  Museum  of  Natural  History — Geology,  Vol.  IV. 

Jaekel,  apparently  is  comparable  to  the  angular  of  the  Teleostomi. 
The  term  angular  may  therefore  properly  be  employed  for  it. 

As  is  fully  evident  from  the  facts  now  known,  the  jaws  in  the 
Arthrodires  must  have  been  homologous  with  those  in  other  fishes,  and 
their  movements,  as  emphasized  by  Woodward  (1922,  p.  35),  have 
been  as  normally  up  and  downr  (For  the  previous  views  on  this  sub- 
ject see:  Dean  1901,  pp.  105-107;  Hussakof  1906;  Jaekel  1919, 
pp.  96-108;  Adams  1919,  pp.  123-127.) 

In  Erromenosteus  (Jaekel  1919,  Fig.  9)  the  ventral  parts  of  the 
hyoid  arch  and  perhaps  also  a  basibranchial  element  appear  to  have 
been  ossified. 

Dentition 

Teeth  are  found  in  all  young  specimens  of  Coccosteids,  but  while 
in  certain  forms,  as  for  instance,  Coccosteus  and  Diplognatus,  they 
are  retained  throughout  life,  they  are  in  adult  specimens  of  several 
other  forms  such  as  Dinichthys,  Titanichthys  etc.,  entirely  abraded  by 
use,  the  labial  edges  of  the  jaws  becoming  in  these  forms  transformed 
to  cutting  edges  or  adapted  for  crushing. 

It  is  generally  maintained  (Cf.  Woodward  1922,  p.  35)  that  the 
teeth  occur  in  a  single  series  on  the  labial  margins  of  the  jaws,  but 
the  investigations  undertaken  by  the  author1  show  that  on  the  mixi- 
coronoid  of  certain  forms  there  is  at  least  a  second  and  perhaps  also  a 
third  or  more  series  of  lower  teeth  medially  of  the  labial  ones.  All  the 
teeth  are  ankylosed  to  the  jaw  bones  with  their  bases  and  generally  have 
the  central  parts  occupied  by  a  rather  large  pulp-cavity.  In  the  dorsal 
parts  this  pulp-cavity  is  generally  surrounded  by  ortho-dentine,  in  the 
basal  parts  by  trabecular-dentine,  but  in  certain  teeth  the  trabecular- 
dentine  may  extend  almost  to  the  apex.  This  seems  especially  to  be 
the  case  in  one  category  of  large  teeth  which  belong  to  the  labial 
series  and  are  characterized  by  the  fact  that  they  have  on  their  medial 
side  one,  two  or  three,  small,  bluntly  conical  cusps.  Basally  the  tra- 
becular-dentine gradually  turns   into  the  bone   of   the  mixicoronoid. 

Externally  of  the  dentine  there  is  in  the  distal  parts  of  the  teeth  a 
layer  of  bright,  shining  enamel,  which  is  perforated  by  the  distal  ex- 
tensions of  the  dentine  tubules,  these  tubules  leading  to  and  opening 
on  the  outside  of  the  enamel.  Also,  the  cusps  on  the  medial  side  of 
the  large  external  teeth  are  provided  with  an  enamel  layer  of  the  same 
sort.  Besides  the  cusps  on  the  medial  side,  several  of  the  larger  teeth 
of  the  external  series  have  also  a  small  cusp  on  the  anterior  and  pos- 

'The  investigations  have  been  made  on  the  mixicoronoid  of  a  Coccosteid  from 
the  Devonian  of  Spitzbergen. 


Macropetalichthyids  and  other  Arthrodires — Stensio     177 

terior  side,  so  that,  when  seen  from  the  lateral  or  medial  side,  they 
have  the  appearance  of  shark  teeth  (also  teeth  of  Acanthodians). 

The  occurrence  of  at  least  two  or  three  longitudinal  series  of  teeth 
in  their  jaws,  together  with  the  circumstance  that  certain  of  the  teeth 
in  the  external  one  of  these  series  are  shark-like  in  shape,  indicates  that 
the  dentition  in  the  Coccosteids  probably  has  arisen  from  an  Elasmo- 
branchian-like  one.1  An  additional  support  for  this  view  is  the  fact 
that  the  medial  side  of  the  mixicoronoid  ventrally  of  the  longitudinal 
series  of  teeth  appears  to  consist  mainly  of  a  dentine-like  tissue. 

Sensory   Canals  of  the   Head 

The  sensory  canal  system  of  the  Coccosteids  is,  as  in  that  of  the 
Phlyctenaspids,  represented  merely  by  grooves  on  the  external  sur- 
faces of  certain  of  the  external  dermal  bones.  The  course  of  these 
grooves  is  best  known  in  Coccosteus  dccipiens  (Figs.  24  A,  25)  and 
in  the  Dinichthys  species  (Fig.  24  B).  The  subsequent  account  is  based 
chiefly  on  C.  decipietis. 

The  supraorbital  groove  (soc,  Figs.  24  A,  B;  25)  goes  from  the 
plate  B  forward  and  somewhat  laterally  to  the  plate  A,  which  it  crosses 
to  the  antero-lateral  corner.  From  this  point  it  continues  downward 
anterior  of  the  eye  and  posterior  to  the  nasal  aperture  on  the  plate  L, 
on  which  it  probably  anastomized  with  the  infraorbital  groove.  It  is 
thus  fully  evident  that  with  its  anterior  part  it  had  the  same  course 
as  in  the  recent  Elasmobranchs  (Cf.  Allis  1901,  pp.  104-107;  1905). 

The  infraorbital  groove  (ifc,  Figs.  24  A,  B,  25)  has  on  the  dermal 
cranial  roof  exactly  the  same  course  as  in  the  Phlyctenaspids  and  has 
also  a  postero-medial  branch  (ifbr),  as  in  these.  We  can  here  see 
quite  clearly  from  its  transverse  course  that  this  branch  cannot 
represent  a.  part  of  the  supraorbital  groove  as  one  might  perhaps  be 
inclined  to  think  merely  from  its  position  in  the  Phlyctenaspids  (Cf . 
Pollard  1892b,  pp.  546-548).  From  the  dermal  cranial  roof  the  in- 
fraorbital groove  turns  latero- ventrally  to  the  cheek,  on  which  it  is 
first  situated  on  the  infraorbital  bone.  On  this  it  passes  first  down- 
wards and  then  anteriorly  in  the  normal  way,  posterior  and  ventrally  of 
the  orbital  entrance.  After  leaving  the  infraorbital  it  continues  for- 
ward on  the  plate  L,  probably  anastomizing  there  with  the  supraorbital 
groove  and  probably  passing  anterior  of  this  commissure  ventrally  of 
the  nasal  aperture.  What  its  relations  were  at  the  very  anterior  end 
is  not  known. 

JThe  only  description  that  I  have  found  of  the  microscopic  structure  of  the 
teeth  in  Coccosteids  was  published  by  Agassiz  1844  (p.  26).  What  Agassiz 
describes  there  is  probably  merely  a  basal  part  of  a  tooth. 


178    Field  Museum  of  Natural  History — Geology,  Vol.  IV. 

The  cephalic  division  of  the  lateral  line  groove  (Ic,  Figs.  24  A,  B, 
25)  has  the  same  course  as  in  the  Phlyctenaspids.  Close  to  its  pos- 
terior end  there  issues  from  its  medial  side  a  branch  (xp)  in  anterior 
and  somewhat  medial  direction.  This  branch,  which  goes  close  to 
the  medial  edge  of  the  bone-plate  6"  and  which,  contrary  to  what  is 
,  shown  in  most  restorations,  is  Tather  short  and  does  not  reach  the  plate 
B,  may  perhaps  correspond  to  a  lateral  part  of  the  supratemporal  cross 
commissure. 

The  preopercidar  groove  (poc,  Figs.  24  A,  B,  25)  issues  in  the 
plate  Pi  from  the  point  where  the  infraorbital  groove  and  the  lateral 
line  groove  meet  each  other,  quite  as  it  does  in  the  Macropetalichthyids 
and  Phlyctenaspids.  It  goes  to  or  close  to  the  postero-lateral  corner 
of  the  cranial  roof,  its  passage  on  the  cheek  being  unknown,  as  it 
probably  passed  there  entirely  in  soft  tissue. 


Fig.    25.       COCCOSTEUS    DECIPIENS 

Head  and  abdominal  armour,  chiefly  from  Jaekel  (1902).  Sensory  canal 
grooves  indicated  by  double  dotted  lines  and  colors. 

A,  B,  J,  L,  Pi,  P2,  R,  S,  bones  of  the  dermal  cranial  roof ;  Ps,  So,  bones 
of  the  cheek  (So,  infraorbital  bone);  Mx,  maxillary;  Pmx,  premaxillary ;  Mix, 
mixicoronoid ;  Spi,  spinal;  ifc,  infraorbital  groove  (blue);  ifbr,  postero-medial 
branch  of  the  infraorbital  (blue)  ;  juc,  /ugal  groove  (yellow)  ;  Ic,  cephalic 
division  of  the  lateral  line  (red)  ;  mp,  groove  probably  corresponding  to  the 
middle  head-line  of  pit  organs  (red)  poc,  preopercular  groove  (yellow);  pp, 
groove  probably  corresponding  to  the  posterior  head-line  of  pit  organs  xp,  groove 
probably  corresponding  to  a  lateral  part  of  the  supratemporal  cross  commissure. 

About  at  the  place  in  the  infraorbital  plate  (So)  at  which  the  in- 
fraorbital groove  turns  forward  from  its  downward  direction,  there 
issues  from  it  a  posteriorly  and  somewhat  ventrally  running  branch 
(juc,  Figs.  24  A,  B;  25)   which  obviously  is  the  homologue  of  the 


Macropetalichthyids  and  other  Arthrodires — Stensio     179 

horizontal  cheek  canal  of  the  Elasmobranchs  (Allis  1923,  pp.  199- 
201),  the  horizontal  part  of  the  jugal  canal  of  Crossopterygians 
(Stensio  1921,  pp.  76-7711923,  p.  1258),  the  horizontal  cheek  line  of 
several  Teleostomous  fishes  (Allis  1889,  p.  506,  PI.  42;  1900,  p.  445; 
1905,  pp.  406-407;  1923  p.  201,  Pollard  1892b,  p.  548)  and  the  jugal 
groove  of  the  Stegocephalians  (Moodie  1908,  p.  515;  1915,  p.  320). 

Whether  there  was  any  mandibular  canal  is  not  known. 

Behind  the  postero-medial  branch  of  the  infraorbital  groove,  too, 
paired,  short  grooves  (Figs.  24,  25)  are  regularly  found  on  the  bone 
plate  B  in  most  of  the  Coccosteids  examined  by  the  author.  The 
anterior  one  (mp)  of  these  grooves  is  situated  transversally  to  the 
longitudinal  axis  of  the  head  and  seems  to  correspond  to  the  middle 
head-line  of  pit  organs  in  the  Elasmobranchii  and  Teleostomi,  while 
the  posterior  one  (pp)  which  is  situated  obliquely  so  that  its  anterior 
end  is  nearer  to  the  median  line  than  the  posterior  one,  probably  is 
homologous  with  the  posterior  head-line  of  pit  organs  in  the  same  fishes. 
(Cf.  Allis  1889,  pp.  502-509,  PI.  42;  Herrick  1901,  pp.  222-223,  PI. 
14;  Stensio  1921,  p.  218;  1923,  p.  1258;  etc.) 

Some  Remarks  on  the  Trunk  and  the  Fins1 

A  pectoral  spine  (Spi,  Fig.  25)  although  much  smaller  than  in  the 
Phlyctenaspids,  occurs  at  least  in  most  of  the  Coccosteids,  and  it  is 
beyond  question  that  the  paired  plate  found  in  Coccosteus  decipiens  and 
Dinichthys  gouldi  somewhat  behind  the  abdominal  armour,  really  rep- 
resents the  pelvic  girdle  (Cf.  Woodward  1891,  pp.  282,  289;  1922,  p. 
35;  Dean  1896,  p.  162;  1909,  pp.  282-287).  There  are  also  in  C. decip- 
iens a  few  endoskeletal  radials  in  connection  with  the  pelvic  girdle.  The 
lateral  line  was,  on  the  trunk  at  least,  partly  surrounded  by  lime-bear- 
ing tissue,  but  whether  this  tissue  was  bone  or  not  it  is  not  possible 
to  say.  There  are  also  in  certain  well-preserved  specimens  reliable  evi- 
dences of  very  delicate  dermal  tubercles  behind  the  abdominal  armour. 

Contrary  to  what  is  generally  maintained,  I  feel  inclined  to  think 
that  the  pelvic  girdle,  as  well  as  all  other  endoskeletal  elements  that 
are  found  preserved  in  Coccosteids,  consists  of  true  bone.  A  more 
detailed  microscopic  examination  of  these  elements  has,  however,  so 
far  not  been  made,  a  fact  which  is  much  to  be  regretted. 

'The  remarks  given  here  on  the  skeleton  of  the  pelvic  girdle  and  fins  of 
Coccosteus  are  based  on  observations  made  by  the  author  in  the  Royal  Scottish 
Museum,  Edinburgh  and  the  British  Museum,  London.  I  fully  agree  with  Wood- 
ward (1891)  in  his  interpretation  of  the  specimens  in  the  latter  museum 
(Dean  1909,  p.  285). 


180    Field  Museum  of  Natural  History — Geology,  Vol.  IV. 

Some  General  Remarks  on  the  Coccosteids 
From  what  we  know  at  present  of  the  Coccosteids,  it  seems  as  if 
they  degenerated  during  the  Devonian  with  regard  to  the  degree  of 
ossification  both  in  the  exo-  and  endo-  skeleton,  a  fact  which  to  a  cer- 
tain degree  was  emphasized  by  Jaekel  in  1906  (1906a  p.  82).  In 
connection  with  this  also  a  reduction  of  the  pectoral  spines  took  place. 

THE  HOMOSTEIDS 

The  Homosteids,  represented  by  the  genus  Homosteus,  are  certainly 
closely  related  to  the  Coccosteids. 

The  bones  of  the  dermal  cranial  roof  are  the  same  as  in  the  Coccos- 
teids, but  the  dermal  cranial  roof  as  a  whole  differs  from  that  in  these 
by  the  considerable  lengthening  of  the  occipital  region  and  by  the  fact 
that  the  orbital  entrance  is  directed  upwards  and  entirely  situated  in 
it.  It  thus  approaches  in  these  respects  that  of  the  Phlyctenaspids  on 
the  one  hand  and  that  of  the  Macropetalichthyids  on  the  other. 

The  plate  L  is  not  found  in  Traquair's  restoration  (Traquair 
1889)  of  the  fish,  a  circumstance  which  probably  indicates  that  it  had 
become  entirely  reduced.  The  anterior  parts  of  the  plates  Px,  A  and  R 
lack  both  ornament  and  sensory  canal  grooves  and  must  obviously  have 
been  situated  deep  in  the  skin  and  are  probably  in  an  early  stage  of  re- 
duction. The  other  parts  of  the  dermal  cranial  roof  are  provided  with 
a  faint  ornament,  and  this,  in  connection  with  the  fact  that  certain 
of  the  sensory  canal  grooves  are  lacking,  while  the  remaining  ones 
are  rather  shallow  and  indistinct,  seems  to  indicate  that  the  dermal  cra- 
nial roof  as  a  whole  had  commenced  to  sink  down  into  the  deeper  layers 
of  the  skin. 

The  skeleton  of  the  cheek  and  the  visceral  skeleton  are  very  im- 
perfectly known  and  nothing  can  therefore  be  said  of  them  here. 

THE  MYLOSTOMIDS 

The  Mylostomids,  which  probably  are  to  be  considered  as  an  highly 
specialized  offshoot  of  the  Coccosteids,  differ  from  them  mainly  in  the 
characters  of  their  dentition,  the  teeth,  as  we  know,  being  in  them 
transformed  to  strong  tritoral  plates. 

The  dermal  cranial  roof  is,  at  least  in  Mylostoma,  said  to  be  thin 
and  devoid  of  ornament  and  lacks  most  of  the  sensory  canal  grooves, 
all  of  which  conditions  indicate  that  it  was  situated  deep  in  the  skin 
and  probably  was  in  an  initial  stage  of  reduction.  It  may  further  be 
mentioned  that  the  plates  homologous  with  L  and  Ps  of  Coccostens 
are  lacking  and  that  the  infraorbital  plate  (So)  is  narrow.  The  orbital 
opening  is  not  directly  limited  by  any  part  of  the  dermal  cranial  roof. 


Macropetalichthyids  and  other  Arthrodires — Stensi5     181 

In  the  lower  jaw  of  Dinomylostotna,  the  Meckelian  cartilage  is  ossi- 
fied in  the  pars  articularis  (Woodward  1922,  p.  34;  Eastman  1906, 
pp.  25-26).  Eastman's  view  that  the  tritoral  dentition  of  the  Mylos- 
tomids  would  be  more  primitive  than  that  in  the  Coccosteids  (East- 
man 1906,  p.  6;  1907;  1908a,  p.  95;  1908b,  p.  163)  must,  as  is  easily 
understood,  be  incorrect  (Cf.  Woodward  1922,  p.  35),  for  the  Mylos- 
tomids  not  only  do  not  pertain  to  the  latest  Arthrodires  (they  are 
from  the  upper  Devonian),  but  they  appear  in  most  respects  to  be 
more  specialized  than  the  Coccosteids  from  the  lower  Devonian.  More- 
over it  would  be  very  difficult  to  explain  from  Eastman's  point  of 
view  how  the  tritoral  plates  of  the  Mylostomids  could  be  transformed 
into  teeth  of  the  type  found  in  the  more  primitive  Coccosteids,  as,  for 
instance,  in  Coccostcus. 

THE  PTYCTODONTIDS 

The  primordial  neurocranium  of  Rhamphodus  is  said  by  Jaekel 
(1906b,  p.  183)  to  consist  of  calcified  cartilage,  and  if  I  understand 
Jaekel's  account  correctly  this  would  also  have  been  the  case  with 
the  visceral  skeleton.  I  am  not  inclined  to  accept  this  view,  however, 
but  rather  think  that  we  are  in  this  case  as  in  the  Macropetalichthyids 
concerned  with  true  bone-tissue.  Probably  this  bone-tissue,  as  in 
Macropetalichthys,  appeared  chiefly  or  exclusively  as  thin  perichondral 
layers  without  evidence  of  sutures  and  distinct  centres,  conditions  which 
of  course  without  microscopic  investigation  make  the  detection  of  its 
true  nature  difficult. 

I  have  more  reason  to  suspect  that  the  primordial  skeleton  of 
Rhamphodus  was,  at  least  in  part,  actually  ossified,  since  the  primor- 
dial neurocranium  in  a  form  pertaining  to  the  family  dealt  with  below 
after  the  Ptyctodontids,  as  far  as  I  could  find  by  a  macroscopic  exami- 
nation of  it,  was  to  a  considerable  extent  ossified,  although  it  is  said 
by  Jaekel  in  a  recent  paper  (1921,  p.  217)  to  consist  of  calcified 
cartilage   (cf.  the  Jagorinids  below)1. 

Jaekel  further  mentions  a  "Schadeldach"  in  Rltamphodus,  which, 
if  I  understand  him  correctly,  must  mean  that  there  is  in  this  fish  a 
dermal  cranial  roof  (Jaekel  1906b,  p.  183). 

Concerning  the  dentition,  I  have  nothing  new  to  add  here.  It  must, 
however,  be  emphasized  that  it  is  highly  specialized.  On  account  of 
its  agreements  with  that  of  the  Chimaeroids,  the  Ptyctodontids  have, 
as  is  well  known,  been  considered  by  several  authors  to  be  closely  allied 
to  the  Chimaeroids  (Cf.  Eastman  1908b,  pp.  120-123). 

'In  another  place  in  the  same  paper  Jaekel  is,  however,  obviously  aware 
that  it  was  ossified   (Jaekel  1921,  p.  218). 


1 82    Field  Museum  of  Natural  History — Geology,  Vol.  IV. 

Rhamphodus  has  behind  the  head  a  dermal  armour  on  the  anterior 
part  of  the  trunk,  an  armour  that,  as  is  clearly  shown  by  Jaekel,  is  of 
the  Arthrodiran  type  (Jaekel  1906b,  Figs.  3,  5)  although  it  has  become 
more  reduced  than  is  generally  the  case  in  the  Arthrodires.  In  fact 
this  armour  is  represented  merely  by  certain  of  the  anterior  plates 
and  the  pectoral  spine,  which  latter  occupies  its  ordinary  position.  Its 
agreements  with  a  dermal  shoulder  girdle  are  obvious  from  Jaekel's 
account,  and  from  this  it  seems  to  be  beyond  question  that  the  armour 
of  the  trunk  in  the  Arthrodires,  at  least  in  its  anterior  parts,  really  is 
homologous  with  the  dermal  shoulder  girdle  of  the  Telostomi  and 
Tetrapods. 

The  trunk  armour  of  the  Ptyctodontids,  as  is  seen  from  Jaekel's 
figure  of  it,  obviously  formed  part  of  the  posterior  boundary  of  the 
branchial  chamber  and  we  thus  have  here  an  additional  support  for 
my  view  that  this  chamber  in  Arthrodires  did  not  extend  backward 
into  the  trunk.  (Cf.  Jaekel  1906b,  Figs.  3-6;  1907,  p.  184;  the  homo- 
logue  of  the  spinale  also  clearly  understood  from  Jaekel's  figures  3-6 
in  1906a.) 

THE  JAGORINIDS 

In  a  paper  published  in  192 1,  Jaekel  described  under  the  name  of 
Jagorina  pandora,  certain  remains  of  an  upper  Devonian  fish,  which 
in  this  connection  has  a  special  interest.  Through  the  courtesy  of 
Prof.  Jaekel,  I  had,  during  a  visit  at  Greifswald  in  1922,  the  oppor- 
tunity to  examine  the  material  so  far  available  of  this  fish  and  the 
account  given  below  is  therefore  in  part  based  on  my  personal  ob- 
servations. 

Primordial  Neurocranium 

The  primordial  neurocranium  is  said  by  Jaekel  in  one  part  of  his 
paper,  as  already  pointed  out  above,  to  consist  of  calcified  cartilage, 
while  in  another  part  it  is  said  to  have  its  outer  and  inner  walls 
feebly  ossified.  From  the  detailed  account  given  by  Jaekel  and  from 
my  own  observations  it  is,  however,  fully  evident  to  me  that  we  are 
concerned  here  with  a  primordial  neurocranium  that  consisted  chiefly 
of  cartilage,  but  which  had  the  outside  and  inside  (cerebral  side)  of 
this  cartilage  provided  with  a  thin,  perichondral  layer  of  bone  exactly 
as  in  Macropetalichthys  rapheidolabis.  There  were,  also,  as  in  this 
species,  a  labyrinth  layer  of  perichondral  bone  and,  at  least,  to  a  cer- 
tain extent,  canal  layers  too. 

Unfortunately  the  single  specimen  that  exhibits  the  primordial 
neurocranium  is   preserved   so   that   the   primordial   neurocranium   is 


Macropetalichthyids  and  other  Arthrodires — Stensio     183 

available  for  examination  chiefly  from  the  ventral  side.  The  shape 
from  this  side  is  shown  by  Fig.  26,  which  has  been  copied  after  Jaekel. 
As  is  seen  from  this  figure  the  ethmoidal  region  is  very  short  and 
broad,  with  a  truncated,  concave  anterior  margin  and  a  large  antero- 
lateral^ projecting  process  on  each  side,  a  process  {olf,  Fig.  26), 
which  obviously  is  so  situated  and  has  such  a  shape,  that  it  agrees 
completely  with  the  olfactory  capsule  of  the  Macropetalichthyids,  and 
is  therefore  undoubtedly  to  be  interpreted  as  the  olfactory  capsule. 
The  orbits  are  very  large  and  imperfectly  bounded  and  the  long  orbito- 
temporal region  is  consequently  not  distinctly  marked  off  from  the 
labyrinth  region,  which  probably  also  is  rather  long.  The  labyrinth 
region  is  further  characterized  by  the  circumstance  that  it  is  broadest 


Fig.  26.    Jagorina  pandora  Jaekel 

Primordial  neurocranium  in  ventral  view.    After  Jaekel    (1921).    XH-    c°, 
occipital  condyle   (paired);  olf,  nasal  capsule;  orb,  orbit. 

in  its  posterior  parts,  quite  as  the  one  in  Dinichthys  (Cf.  Fig.  23  B). 
The  occipital  region  is  short  and  its  posterior  end  is  provided  with  a 
paired  condyle  for  articulation  with  the  vertebral  column. 

As  a  bottom  for  the  orbit  does  not  occur  in  the  fish  and  the  interor- 
bital  wall  is  fairly  narrow  in  comparison  with  that  in  the  Macropetali- 
thyids,  we  must  expect  that  the  carotis  interna  passed  forward  along 
the  lateral  edge  of  the  ventral  side  of  the  primordial  neurocranium  and 
not  in  the  orbital  bottom  as  in  Macropetalichthys  rapheidolabis.  Con- 
sequently it  is  probable  that  this  artery  when  it  turned  medially  to 
ascend  through  the  ventral  wall  of  the  primordial  neurocranium  to  the 
cavum  cerebrale,  entered  a  canal  which  opened  in   one  of  the  pits 


1 84    Field  Museum  of  Natural  History — Geology,  Vol.  IV. 

situated  on  the  ventral  side  of  the  anterior  part  of  the  primordial  neuro- 
cranium  at  about  the  transition  between  the  orbitotemporal  and  ethmoid- 
al regions.  (As  these  pits  had  not  been  cleaned  from  matrix  in  their 
deeper  parts  at  the  time  I  examined  the  specimen,  I  cannot,  however, 
say  with  certainty  whether  there  were  among  them  any  that  really 
formed  ventral  openings  for  canals  of  this  sort.) 

The  labyrinth  cavity  is  well  preserved  and  is  evidently  entirely 
separated  from  the  cavum  cerebrale,  quite  as  in  M.  rapheidolabis  and 
Selachians.  The  separating  wall,  which  consisted  of  cartilage,  was 
lined  by  the  internal  bone  layer  on  the  cerebral  surface  and  the 
labyrinth  bone  layer  on  the  labyrinth  surface.  A  division  for  the 
sacculus,  divisions  for  semicircular  canals  and  a  dorsally  ascending 
canal  for  the  ductus  endolymphaticus  are  clearly  distinguishable.  The 
canal  for  the  ductus  endolymphaticus  opened  on  the  dorsal  side  of  the 
primordial  neurocranium  and  it  seems  probable  also  that  in  the  living 
fish  it  continued  out  to  and  opened  on  the  external  surface  of  the  skin, 
as  it  does  in  Epipetalichthys  wildungensis,  Selachians  and  Chimaeroids. 
The  canal  for  the  n.  acusticus  issues  from  the  cavum  cerebrale  very  low 
down,  almost  at  the  bottom  and  goes  outward  to  the  ventral  parts  of 
the  labyrinth  cavity,  probably  almost  as  in  M .  rapheidolabis. 

The  shape  of  the  caVum  cerebrale  is  imperfectly  known,  but,  as 
far  as  can  be  judged  at  present,  it  appears  to  have  resembled  that  in 
M.  rapheidolabis. 

What  function  is  to  be  ascribed  to  the  wide  canal  that  opens  on,  the 
posterior  side  of  the  labyrinth  region  (Fig.  26)  it  is  not  possible  to 
decide  at  present,  as  its  course  inside  the  lateral  wall  is  very  imper- 
fectly known.  It  appears  most  probable  that  it  may  have  transmitted 
the  jugular  vein,  and  perhaps,  also,  in  its  posterior  parts,  the  vagus 
nerve  as  well. 

It  is  fully  evident  that  the  palatoquadrate  cannot  have  been  fused 
with  the  primordial  neurocranium,  but  must  have  been  an  independent 
element. 

Despite  the  fact  that  the  primordial  neurocranium  of  Jagorina 
pandora  is  still  in  several  points  imperfectly  known,  we  see,  however, 
that  it  is  clearly  of  the  Arthrodiran  type  (Cf.  Fig.  23).  It  is  therefore 
beyond  question  that  Jagorina  pandora  cannot  be  a  sturgeon,  as  main- 
tained by  Jaekel,  but  that  it  must  be  referred  to  the  Arthrodires. 

Dermal  Cranial  Roof 
The  dermal  cranial  roof  is,  as  far  as  is  known,  represented  merely 
by  feebly  developed  isolated  tubercules   (called  "Dornen"  in  the  de- 
scription given  by  Jaekel  1921,  p.  219).     The  microscopic  structure 


Macropetalichthyids  and  other  Arthrodires — Stensio     185 

of  these  tubercles  is  not  known  and  it  is  therefore  impossible  to  say 
whether  they  consist  of  bone  or  whether  they  are  most  comparable 
to  the  dermal  denticles  of  the  sharks. 

This  fish  thus  has  no  real  dermal  cranial  roof  of  bones  united  with 
each  other  by  sutures.  The  lack  of  a  cranial  roof  of  this  kind  must, 
however,  as  far  as  we  can  judge,  be  due  to  reduction,  since  a  real  dermal 
cranial  roof  occurs  in  all  the  other  Arthrodires  and  is  generally  even 
most  complete  in  the  forms  from  the  lower  Devonian. 

Dermal  Bones  of  the  Cheek 

No  dermal  structures  belonging  to  the  cheek  have  been  observed 
hitherto. „ 

Visceral  Skeleton 

Associated  with  the  primordial  neurocranium  are  found  several 
remains  of  the  visceral  skeleton,  which  was  partly  ossified.  Among 
these  remains  are  surely  parts  of  the  palatoquad rates  and  the  mandibles. 
It  is  worthy  of  notice  that  the  primordial  neurocranium,  as  far  as  can 
be  seen,  has  no  articulating  surfaces  for  the  anterior  ends  of  the 
palatoquadrates,  and  it  therefore  seems  as  if  these  had  been  suspended 
by  ligaments  beneath  the  ethmoidal  region,  as  in  the  Elasmobranchs. 

Dentition 

The  dentition  is,  as  Jaekel  pointed  out  to  me  during  my  visit  at 
Greifswald,  very  interesting,  as  it  consists  of  numerous,  small,  inde- 
pendent1 Selachian-like  teeth,  thus  teeth  with  several  cusps.  The  shape 
of  these  teeth  is  in  fact  of  such  a  nature  that  they  undoubtedly  would 
have  been  taken  for  shark  teeth  if  they  had  been  found  detached  from 
the  specimen,  a  fact  which  in  this  connection  is  of  much  importance, 
as  it  forms  a  strong  additional  support  for  the  view  advanced  by  me 
in  this  paper  that  the  Arthrodires  are  really  closely  related  to  the  Elas- 
mobranchs.   The  microscopic  structure  of  the  teeth  is  not  known. 

It  is  worthy  of  notice  in  this  connection  that  Woodward  already  in 
192 1  shortly  after  Jaekel  had  published  his  description  of  the  pri- 
mordial neurocranium  of  Jagorina  pandora,  without  any  knowledge  of 
the  character  of  the  dentition,  arrived  at  the  conclusion  that  /.  pandora 
was  a  primitive  shark  (Woodward  1921,  p.  33). 

Sensory  Canals 
Nothing  is  known  of  the  sensory  canals  of  the  head. 

Abdominal  Armour 
Close  behind  the  head  there  is  a  girdle  of  dermal  plates  that  evi- 
dently represents  the  shoulder  girdle.     It  is  not  known  in  detail,  but 

*Not  ankylosed  with  the  jaws 


1 86    Field  Museum  of  Natural  History — Geology,  Vol.  IV. 

Jaekel  says  of  it  (1921,  p.  218)  that  it  is  sturgeon-like,  which  may 
mean  very  little,  since  he  says  the  same  of  that  in  Rhamphodus  (1906b, 
pp.  183-185). 

SOME  GENERAL  REMARKS  ON  THE  NON-MACRO- 
PETALICHTHYID  ARTHRODIRES 

From  what  has  been  set  forth  in  the  account  given  above  the  fol- 
lowing ought  to  be  obvious: 

1.  There  is  strong  reason  to  believe  that  the  primordial  skeleton 
of  the  non-Macropetalichthyid  Arthrodires  originally  was  rather  well 
ossified  and  that  accordingly,  a  reduction  of  the  degree  of  ossification 
took  place  during  the  course  of  the  Devonian  period. 

2.  It  is  fully  clear  that  the  dermal  skeleton  of  the  non-Macropeta- 
lichthyid Arthrodires  was  also  during  the  Devonian  period  in  process 
of  reduction.  In  certain,  especially  upper  Devonian,  forms  the  reduc- 
tion has  gone  rather  far  and  in  Jagorina  even  so  far  that  practically  the 
entire  dermal  skeleton  of  the  head  has  been  lost. 

3.  The  reduction  of  the  dermal  skeleton  in  the  non-Macropetalich- 
thyid Arthrodires  takes  place  in  this  manner :  The  bones  sink  deeper 
into  the  skin,  become  thinner  and  lose  their  ornament  and  the  external 
sensory  canal  grooves.  The  sensory  canals  obviously  must  retain  their 
superficial  relations  to  the  skin  and  they  become  on  this  account  sit- 
uated totally  externally  of  the  bones. 

4.  From  the  facts  so  far  known  it  is  beyond  doubt  that  the  non- 
Macropetalichthyid  Arthrodires  with  regard  to  the  degree  of  ossifica- 
tion represent  a  degenerating  series. 

5.  There  are  so  many  common  points  of  agreement  between  the 
non-Macropetalichthyid  Arthrodires  and  the  Macropetalichthyids  that 
we  cannot  doubt  that  they  are  closely  related  to  each  other  and  that 
they  must,  as  has  generally  been  done  hitherto,  be  referred  to  the 
same  group  of  fishes.  • 

6.  From  the  structure  of  the  primordial  neurocranium,  from  the 
development  of  the  labyrinth  cavity,  from  the  character  of  the  den- 
tition in  certain  forms,  and  from  the  course  and  development  of  the 
sensory  canals,  it  is  clear  that  the  non-Macropetalichthyid  Arthrodires, 
like  the  Macropetalichthyids,  must  be  closely  related  to  the  Elasmo- 
branchs.  In  the  case  of  Jagorina  pandora  this  is  even  so  clear,  that 
we  should  almost  feel  inclined  to  take  it  for  a  primitive  Elasmobranch 
if  we  did  not  know  that  it  had  a  shoulder  girdle  of  dermal  bones. 


Macropetalichthyids  and  other  Arthrodires — Stensio     187 

CONCLUDING  REMARKS  ON  THE  AFFINITIES  OF  THE 

ARTHRODIRES 

After  having  dealt  in  detail  with  the  head  of  the  Macropetalich- 
thyids and  also  given  a  short  account  of  the  head  in  the  other  Arthro- 
dires, I  shall  here  briefly  summarize  the  results  obtained  and  add  cer- 
tain remarks  of  interest  otherwise. 

With  the  comparatively  good  knowledge  we  now  possess  of  their 
anatomy  it  is  quite  clear  that  the  Arthrodires  are  true  fishes  and  that 
as  recently  pointed  out  by  Woodward  (1922,  p.  35)  they  have  noth- 
ing to  do  with  Ostracoderms,  which  as  I  have  been  able  to  make  out, 
are  much  more  lowly  organized  agnathous  vertebrates. 

We  have  seen  that  the  Arthrodires  from  the  oldest  divisions  of  the 
Devonian  generally  have  the  dermal  skeleton  more  complete  and 
stronger  than  those  from  the  youngest  division  of  the  same  formation, 
and  we  have  also  found  that  the  primordial  skeleton  is  more  or  less 
ossified  in  several  of  their  representatives.  Concerning  the  primordial 
skeleton  there  have  been  advanced  several  facts  which  indicate  that  it 
must  have  been  rather  completely  ossified  in  all  primitive  Arthodires. 
Accordingly  we  find  that  the  Arthrodires  like  the  Dipnoi,  the  Crossop- 
terygii,  the  Palaoniscida,  the  Saurichthyida,  the  sturgeon  fishes,  the 
Amiada  and  several  other  fishes,  form  a  degeneration  series  with  re- 
gard to  their  degree  of  ossification. 

In  their  general  organization  the  Arthrodires  have,  as  recently  em- 
phasized by  Woodward  (1922,  p.  35),  little  in  common  with  the  Dipnoi 
and  Crossopterygii,  and  it  is  equally  evident  that  they  are  not  Actino- 
ptcrycjii.  From- the  investigation  made  here  they  were,  however,  found 
to  be  at  the  stage  of  the  Elasmobranchs  and  in  fact  everything  seems 
to  indicate  that  they  are  really  closely  related  to  these.  Their  Elasmo- 
branchian  characters  are  as  follows : 

I.  The  general  characters  of  the  primordial  neurocranium,  especially 
the  tendency  to  broadening  of  the  ventral  surface,  partly  at  the  ex- 
pense of  the  lateral  surfaces.  (This  is  above  all  the  case  in  the  labyrinth 
region,  the  sacculus  having  occupied  about  the  same  position  in  rela- 
tion to  the  ventral  surface  as  in  Chlamydoselachus  and  most  other 
Selachians.)  2.  The  position  and  relations  of  the  olfactory  capsule. 
3.  The  presence  of  a  nasal  fontanelle  on  the  lower  side  of  the  olfactory 
capsule  (Macropctalichtliys)  as  in  Chlamydoselachus  and  certain  other 
Selachians.  4.  The  presence  of  the  cavum  precerebrale  (EpipetalicJi- 
thys).  5.  The  general  shape  of  the  labyrinth,  especially  with  regard 
to  the  position  of  certain  of  its  main  parts,  for  instance,  the  utriculus. 
6.  The  persistence  of  the  ductus  endolymphaticus  (Macropetalichthys, 


1 88    Field  Museum  of  Natural  History — Geology,  Vol.  IV. 

Epipetalichthys,  Jagorina)  and  the  fact  that  there  was  probably,  at 
least  in  certain  forms  (Macropetalichthys) ,  a  fossa  endolymphatica  on 
the  dorsal  side  of  the  primordial  neurocranium  beneath  the  dermal 
bones.  7.  The  fact  that  the  ductus  endolymphaticus,  at  least  in  cer- 
tain forms  (Epipetalichthys),  perforated  the  dermal  cranial  roof  and 
had  an  external  opening  situated  about  as  in  Chlamydoselachus.  8.  The 
general  shape  of  the  brain  as  far  as  this  can  be  restored  from  the  posi- 
tion and  course  of  the  nerve  canals  through  the  cranial  walls  and  from 
the  shape  of  the  cavum  cerebrale.  9.  To  a  certain  extent  the  develop- 
ment of  the  blood  vessels.  10.  The  fact  that  the  palatoquadrate  did 
not  articulate  with  the  ethmoidal  region  but  must  have  been  suspended 
beneath  this  merely  by  ligaments.  II.  The  dentition,  which  in  certain 
forms,  as  Jagorina,  consists  of  multicuspidated  shark-like  teeth.  12.  The 
course  and  development  of  the  sensory  canal  system. 

The  opinion  now  advanced  of  the  close  relationship  between  the 
Arthrodires  and  Elasmobranchs  of  course  implies  either  that  bone  has 
arisen  independently  in  different  groups  of  vertebrates  or  that  it  is  a 
very  old  sort  of  tissue  that  was  present  already  among  the  most  primi- 
tive vertebrates  and  from  these  was  bequeathed  to  the  common  ancestors 
of  the  Arthrodires  and  Elasmobranchs.  As  has  been  pointed  out,  the 
conditions  in  the  Cephalaspids  and  Ostracoderms  in  general  as  well  as 
in  the  Acanthods  and  oldest  Teleostomi  indicate  that  the  latter  alter- 
native ought  to  be  the  true  one,  and  accordingly  that  the  Elasmobranchs 
as  far  as  can  be  understood  at  present  must  have  lost  the  bone-tissue. 
In  other  words  they  too  would  represent  a  degenerating  series  with 
regard  to  the  degree  of  ossification.  In  full  accordance  with  this  view 
is  obviously  the  occurrence  of  large  bone-like  plates  (or  perhaps  true 
bone-plates)  in  the  earliest  known  true  forms  of  the  Holocephali 
(Myriacanthus  and  Chimeeropsis)  and  the  fact  that  among  the  Cochlio- 
dontids  there  is  found  a  form  (Menaspis)  with  evidence  of  armour  on 
the  head  and  anterior  part  of  the  trunk  (Cf.  Woodward  1924)  .* 

Except  by  the  presence  of  bone-tissue  in  their  skeleton,  a  character 
which,  as  we  have  found,  is  of  very  slight  importance  from  a  morpho- 
logical point  of  view,  the  Arthodires  seem,  as  far  as  we  know,  to 
differ  in  no  essential  points  from  the  Elasmobranchs.  The  different 
shape  of  the  vertebral  column  in  them  as  compared  with  the  recent 
Elasmobranchs  might  perhaps  be  considered  very  insignificant,  but  if 
we  consider  the  fossil  Elasmobranchs  this  difference  becomes  less  ap- 

*It  is  also  of  interest  to  note  that  Menaspis  has  paired  lateral  spines,  which 
perhaps  are  identical  with  the  pectoral  spines  of  Arthrodires.  In  fact  it  seems 
not  impossible  that  the  Cochliodontids  will  reveal  themselves  as  highly  special- 
ized Arthrodires  (for  Menaspis  see  Zittel's  Grundzitge  der  Palaeontologie,  1923; 
Dean  1904,  and  Jaekel  1891). 


Macropetalichthyids  and  other  Arthrodires — Stensio     189 

parent,  for  in  the  Palaeozoic  forms  and  certain  earlier  Mesozoic  forms 
of  these  the  neural  arches  are  almost  like  those  in  the  Arthrodires  (Cf. 
Dean  1909,  Clamydosclache;  Fritsch  1895,  Xenacanthus  and  Pleura- 
canthus;  Brown  1900  Hybodus;  Koken  1907,  Hybodus). 

In  addition  to  their  general  Elasmobranchian-like  characters  above 
enumerated  the  Arthrodires  have  also  certain  special  Holocephalian  char- 
acters the  following  of  which  deserve  to  be  specially  mentioned  here. 
1.  The  joint  between  the  head  and  the  vertebral  column.  2.  The 
structure  of  the  branchial  apparatus,  inasmuch  as  this  is  covered  ex- 
ternally by  a  sort  of  gill-cover.  3.  The  character  of  the  dentition  in 
the  more  specialized  forms.  4.  The  dorsal  extension  of  the  pelvic 
girdle.  5.  The  general  shape  of  the  body.  6.  Certain  characters  of  the 
arterial  system. 

Of  these  characters,  No.  3  is  quite  certainly  simply  a  parallelism  and 
it  seems  highly  probable  that  this  is  the  case  with  No.  5  too.  Concern- 
ing the  remaining  four  it  is  difficult  to  say  at  present  how  much  stress 
ought  to  be  laid  on  them,  and  it  is  consequently  difficult  to  conclude 
whether  the  Arthrodires  among  the  Elasmobranchs  were  most  closely 
allied  to  the  Holocephali  or  to  the  Selachii  or  whether  they  represent  an 
independent  branch  from  the  Elasmobranchian  stem.  Since,  as  we  have 
seen,  they  seem  to  have  the  pectoral  fins  much  transformed  or  perhaps 
represented  merely  by  an  anterior  spine,  it  is  not  probable  that  they 
could  have  given  rise  to  the  Holocephali.  If  it  should  appear  that  they 
are  most  closely  allied  to  these  the  Arthrodires  would  have  descended 
from  the  same  primitive  ancestors  or,  if  we  want  to  express  it  more 
exactly,  from  the  primitive  forms  of  the  Holocephalian  branch  of  the 
Elasmobranchian  stem.  Under  the  present  conditions  we  can,  however, 
with  assurance  only  say  that  they  are  to  be  considered  as  an  offshoot  of 
the  Elasmobranchian  stem  of  fishes  and  that  besides  their  Elasmo- 
branchian characters  they  have  retained  a  few  primitive  ones  at  the 
same  time  that  they  by  specialization  have  acquired  certain  new  ones. 

Their  main  primitive  characters  must,  as  far  as  we  understand,  be 
the  presence  of  bone-tissue  in  their  skeleton  and  the  occurrence  of  a 
postero-medial  branch  for  the  infraorbital  sensory  groove  on  the  der- 
mal cranial  roof. 

As  in  another  paper  I  shall  give  a  detailed  account  of  the  relation- 
ship between  the  Arthrodira  and  the  Antiarcha,  I  shall  here  only  men- 
tion that,  as  far  as  I  can  see  from  the  investigations  of  material  in  the 
chief  American  and  European  Museums,  as  well  as  from  material  re- 
cently obtained  from  Scaumenac  Bay,  the  Antiarcha  seem  to  be  a  highly 
specialized  group  of  fishes  closely  related  to  the  Arthrodira. 


BIBLIOGRAPHY 

Adams,  L.  A. 

1919.  A  memoir  on  the  phylogeny  of  the  jaw  muscles  in  recent  and  fossil 
vertebrates.     New  York.    Acad.  Sci.,  Ann.,  Vol.  28. 

Acassiz,  J.  L.  R. 

1844.  Monographic  des  Poissons  Fossiles  Du  Vieux  Gres  Rouge  ou  Systeme 
Devonien   (Old  Red  Sandstone)    Des  lies  Brittaniques  Et  De  Russie. 

Allen,  W.  F. 

1905.  The  blood-vascular  system  of  the  Loricati,  the  mail-cheeked  fishes. 
Washington  Acad.   Sci.,  Proc.,  Vol.  7. 

Allis,  E.  Ph. 

1889.  The  anatomy  and  development  of  the  lateral  line  system  in  Amia  calva. 
Journ.  Morph.,  Vol.  2. 

1897.  The  cranial  muscles  and  cranial  and  first  spinal  nerves  in  Amia  calva. 
Journ.  Morph.,  Vol.  12. 

1898.  On  the  morphology  of  certain  of  the  bones  of  the  cheek  and  snout  of 
Amia  calva.    Journ.  Morph.,  Vol.  14. 

1899.  On  certain  homologies  of  the  squamosal  intercalar,  exoccipital  and 
extrascapular  bones  of  Amia  calva.     Anat.  Anz.,  Bd.  16. 

1900.  The  lateral  sensory  canals  of  Polypterus  bichir.     Anat.  Anz.,  Bd.   17. 

1001.  The  lateral  sensory  canals,  the  eye-muscles,  and  the  peripheral  distribu- 
tion of  certain  of  the  cranial  nerves  of  Mustelus  Icevis.  Quart.  Journ.  Micr. 
Sci.,  Vol.  45. 

1003.     The  skull,  and  the  cranial  and  first  spinal  muscles  and  nerves  in  Scomber 

scomber.    Journ.  Morph.,  Vol.  18. 
1005.     The  latero-sensory  canals  and  related  bones  in  fishes.     Internat.  Monat- 

schrift  f.  Anat.  u.  Physiol.,  Bd.  21. 
1908a.     The  pseudobranchial  and  carotid  arteries  in  Amcirus.  Anat.  Anz.,  Bd.  33. 
1908b.     The  pseudobranchial  and  carotid  arteries  in  Polypterus.     Anat.   Anz., 

Bd.  33. 
1909a.     The  cranial  anatomy  of  the  mail-cheeked  fishes.     Zoologica,  Vol.  22. 
1909b.     The   pseudobranchial   and   carotid   arteries   in    the    gnathostome    fishes. 

Zool.  Jahrb.  Abt.  Anat.,  Bd.  27. 
1911a.     The  pseudobranchial  and  carotid  arteries  in  Polyodon  spathula.     Anat. 

Anz.,  Bd.  39. 
1911b.     The  pseudobranchial  and  carotid  arteries  in  Chlamydosclachus  anguineiu. 

Anat.  Anz.,  Bd.  39. 
1912a.     The  branchial,  pseudobranchial  and  carotid  arteries  in  Chimera  (Hydro- 

lagus)  colliei.    Anat.  Anz.,  Bd.  42. 
1912b.      The    branchial,    pseudobranchial    and    carotid    arteries    in    Hcptanchus 

(Notidanus)  cinerens.    Anat.  Anz.,  Bd.  41. 
1912c.     The  branchial,   pseudobranchial   and   carotid   arteries    in   Raja   radiata. 

Anat.  Anz.,  Bd.  44. 
I9i2d.     The  pseudobranchial  and  carotid  arteries  in  Esox,  Salmo  and  Gadus, 

together  with  a  description  of  the  arteries  in  the  adult  Amia.     Anat.  Anz., 

Bd.  41. 
191 3.     The  homologies  of  the  ethmoidal  region  of  the  Selachian  skull.     Anat. 

Anz.,  Bd.  44. 
1914a.     The  pituitary  fossa  and  trigemino-facialis  chamber  in  Selachians.   Anat. 

Anz.,  Bd.  46. 
1914b.     The  pituitary   fossa  and  trigemino-facialis  chamber  in   Ceratodus  for- 

steri.    Anat.  Anz.,  Bd.  46. 

191 


192     Field  Museum  of  Natural  History — Geology,  Vol.  IV. 

1914c.  Certain  homologies  of  the  palatoquadrate  of  Selachians.  Anat.  Anz., 
Bd.  45- 

1915.  The  homologies  of  the  hyomandibula  of  the  gnathostome  fishes.  Journ. 
Morph.,  Vol.  26. 

1918a.  The  myodome  and  trigemino-facialis  chamber  of  fishes,  etc.  Washing- 
ton.    Nat.  Acad.  Sci.,  Proc,  Vol.  4. 

1918b.  On  the  origin  of  the  hyomandibula  of  the  Teleostomi.  Anat.  Record, 
Vol.  15. 

1918c.  The  ophthalmic  nerves  of  gnathostome  fishes.  Journ.  of  Comp. 
Neurology,  Bd.  30. 

1919a.  The  myodome  and  trigemino-facialis  chamber  of  fishes  and  the  cor- 
responding cavities  in  higher  vertebrates.     Journ.  Morph.,  Vol.  32. 

1919b.     The  homologies  of  the  squamosal  bone  of  fishes.    Anat.  Record,  Vol.  17. 

1920.  The  branches  of  the  branchial  nerves  of  fishes,  with  special  reference 
to  Polyodon  spat  hula.    Journ.  of  Comp.  Neurology,  Vol.  32. 

1922a.  The  cranial  anatomy  of  Polypterus,  with  special  reference  to  Polyp- 
terus  bichir.     Journ.  of  Anat.,  Vol.  56. 

1922b.  The  myodome  and  the  trigemino-facialis  chamber  in  the  Coelacan- 
thidae,  Rhizodontidae  and  Palaeoniscidae.     Journ.  of  Anat.,  Vol.  56. 

1923.  The  cranial  anatomy  of  Chlamydoselachus  anguineus.  Acta  Zoologica, 
Bd.  4. 

Brown,  C. 

1900.  Ueber  das  Genus  Hybodus  und  seine  systematische  Stellung.  Palaeonto- 
graphica,  Bd.  44. 

Bryant,  H.  C. 

1918.  Catalog  of  the  fossil  fishes  in  the  Museum  of  the  Buffalo  Soc.  of  Nat. 
Sci.    Buffalo  Soc.  Nat.  Sci.,  Bull.,  Vol.  12. 

Cole,  F.  J. 

1896a.  On  the  cranial  nerves  of  Chimcera  monstrosa,  with  a  discussion  of  the 
lateral  line  system  and  of  the  morphology  of  the  chorda  tympani.  Edin- 
burgh.    Roy.  Soc.  Trans.,  Vol.  38. 

1896b.     On  the  sensory  and  ampullary  canals  of  Chimcera.    Anat.  Anz.,  Bd.  12. 

1898.  Observations  on  the  structure  and  morphology  of  the  cranial  nerves  and 
lateral  sense  organs  of  fishes ;  with  special  reference  to  the  genus  Gadus. 
London,  Linn.  Soc,  Trans.   (Zool.),  Vol.  7. 

Cope,  E.  D. 

1891.  On  the  characters  of  some  Palaeozoic  fishes.  U.  S.  Nat.  Mus.,  Proc, 
Vol.  14. 

Danforth,  C.  H. 

1912.     The  heart  and  arteries  of  Polyodon.    Journ.  Morph.,  Vol.  23. 

Daniel,  J.  F. 

1915.     The  anatomy  of   Heterodontus  francisci.     II.  Journ.   Morph.,  Vol.  26. 

Dean,  B. 

1896.  On  the  vertebral  column,  fins  and  ventral  armoring  of  Dinichthys.  New 
York  Acad.  Sci.,  Trans.,  Vol.  15. 

1901.  Palseontological  Notes.     New  York  Acad.  Sci.,  Mem.,  Vol.  2. 

1904.     In  the  matter  of  the  Permian  fish  Menaspis.    Amer.  Geologist,  Vol.  34. 
1909.     Studies  on  fossil  fishes  (Sharks,  Chimseroids,  and  Arthrodires).    Ameri- 
can Mus.  Nat.  Hist.,  Mem.,  Vol.  9. 

Eastman,  Ch.  R. 

1906.  Structure  and  relations  of  Mylostoma.  Cambridge.  Mus.  of  Comp. 
Zool.  Harvard.,  Bull.,  Vol.  50. 


Macropetalichthyids  and  other  Arthrodires — Stensio     193 

1907.     Mylostomid    dentition.      Cambridge.    Mus.    of    Comp.    Zool.    Harvard., 

Bull.,  Vol.  50. 
1908a.     Devonic  fishes  of   the   New  York   formations.     Albany.   N.   Y.    State 

Museum,  60th  Annual  Report,   106,  Vol.  5.     Appendix  7    (continued). 
1908b.    Devonian  fishes  of  Iowa.    Iowa  Geol.  Surv.,  Vol.  18.    Ann.  Rep.  1907. 

Eichwald,  C.  Ed. 

i860.     Lethaea  Rossica.,   1 :2. 

Ewart,  J.  C. 

1892.  The  lateral  sense  organs  of  Elasmobranchs.  I.  The  sensory  canals  of 
Lcemargus.    Edinburgh.    Roy.  Soc,  Trans.,  Vol.  37,  Pt.  I. 

Ewart,  J.  C.  and  Cole,  F.  J. 

1895.  On  the  dorsal  branches  of  the  cranial  and  spinal  nerves  of  Elasmo- 
branchs.   Edinburgh.    Roy.  Soc.,  Proc.,  Vol.  20. 

Ewart,  J.  C.  and  Mitchel,  J.  C. 

1892.  On  the  lateral  sense  organs  of  Elasmobranchs.  II.  The  sensory  canals 
of  the  common  skate   (Rata  batis).     Edinburgh.  Roy.  Soc.,  Trans.,  Vol.  37. 

Fritsch,  A.  J. 
1895.     Fauna   der   Gashohle   u.   der    Kalksteine    der    Permformation    Bohmens, 
Bd.  3.     Prague. 

FURBRINGER,    K. 

1904.  Beitrage  zur  Morphologie  des  Skelettes  der  Dipnoer,  nebst  Bemerkun- 
gen  uber  Pleuracanthiden,  Holocephalen  and  Squaliden  (In  Scmon,  R.  Zoo- 
logische  Forschungsreisen  in  Australien  und  dem  Malayischen  Archipel, 
Bd.  1).     Jena.  Med.  Nat.  Gesellsch.,  Denkschriften  4. 

Garman,  S. 

1888.  On  the  lateral  canal  system  of  the  Selachia  and  Holocephala.  Cam- 
bridge.    Mus.  Comp.  Zool.  Harvard,  Bull.,  Vol.   17. 

Gegenbaur,  C. 

1872.     Untersuchungen  zur  Vergl.  Anat.  der  Wirbelthiere.  III.  Das  Kopfskelet 

der  Selachier,  etc. 
1898.     Vergleichende    Anatomie    der    Wirbelthiere    mit    Berucksichtigung    der 
Wirbellosen.  Bd.  1.  Leipzig. 

1912.  Ueber  die  occipital  region  und  die  ihr  benachbarten  Wirbel  der  Fische. 
Gesammelte  Abhandlungen  von   C.  Gegenbaur.   Bd.   3.   Leipzig. 

Goodey,  A.  T. 

1910.  A  contribution  to  the  skeletal  anatomy  of  the  filled  shark,  Clamydose- 
lachus  anguineus.     London.  Zool.  Soc,  Proc. 

Goodrich,  E.  S. 

1009.  Vertebrata  Craniata,  Fasc.  I :  Cyclostomes  and  Fishes  in  Lankester's 
Treatise  on  Zoology,  Part  IX. 

Greil,  A. 

1913.  Entwicklungsgeschicht  des  Kopfes  und  des  Blutgefassystems  von  Cera- 
todus  fosteri.  Part  2:  Die  epigenetischen  Erwerbungen  wahrend  der 
Stadien  39-48.     Jena.  Med.  Nat.  Gesellsch.,  Denkschr.,  Bd.  4. 

Grosser,  O. 

1907.  Die  Elemente  des  Kopfvenensystems  der  Wirbelthiere.  Verhandl.  Anat. 
Ges.  Supplement.     Anat.  Anz.,  Bd.  30. 

Hawkes,  O.  A. 

1906.  The  cranial  and  spinal  nerves  of  Chlatnydoselachus  anguineus.  London. 
Zool.  Soc,  Proc 


194    Field  Museum  of  Natural  History — Geology,  Vol.  IV. 

Hennig,  E. 

1907.  Macropetalichthys  pelmensis,  n.sp.,  Stuttgart,  Centralbl.  f.  Min.  Geol. 
Pal. 

Herrick,  C.  J. 

1899.  The  cranial  and  first  spinal  nerves  of  Menidia;  a  contribution  upon  the 
nerve  components  of  the  bony  fishes.     Journ.  of  Comp.  Neurology,  Vol.  9. 

1900.  A  contribution  upon  the  cranial  nerves  of  the  codfish.  Journ.  of  Comp. 
Neurology,  Vol.  10. 

1901.  The  cranial  nerves  and  cutaneous  sense  organs  of  the  North  American 
siluroid  fishes.     Journ.  of   Comp.  Neurology,  Vol.   11. 

Hussakof,  L. 

1906.  Studies  on  the  Arthrodira.     Amer.  Mus.  Nat.  Hist.,  Mem.,  Vol.  9. 

Huxley,  Th.  H. 

1864.     Lectures  on  the  elements  of  comparative  anatomy.     London. 

Iwanzow,  N. 

1887.  Der  Scaphirhynchus.  Vergleichendo-anatomische  Beschreibung.  Moscou. 
Soc.  Imper.  des  Nat.,  Bull. 

Jaekel,  O. 

1891.  Ueber  Mcnaspis  armata  Ewald.  Berlin.  Gesellsch.  Naturforsch.  Freunde. 
Sitzber. 

1902.  Ueber  Coccosteus  und  die  Beurtheilung  der  Placodermen.  Berlin. 
Gesellsch.  Naturforsch.  Freunde,  Sitzber. 

1906a.     Neue    Wirbelthierfunde    aus    dem    Devon    von    Wildungen.      Berlin. 

Gesellsch.  Naturforsch.  Freunde,  Sitzber. 
1906b.     Einige   Beitrage   zur   Morphologie   der   altesten   Wirbelthiere.     Berlin. 

Gesellsch.  Naturforsch.  Freunde,  Sitzber. 

1907.  Uber  Pholidosteus  n.g.  Die  Mundbildung  n.  die  Korperform  der  Pla- 
codermen. Berlin.     Gesellsch.  Naturforsch.  Freunde.  Sitzber. 

191 1.     Die  Wirbelthiere.     Berlin. 

1919.     Die   Mundbildung   der   Placodermen.     Berlin.     Gesellsch.     Naturforsch. 

Freunde,  Sitzber. 
1921.     Palaeontologische  Berichte.    II.    Schadelprobleme.    Palaeontologische  Zeit- 

schrift,  Vol.  3. 

Johnston,  J.  B. 

1898.     Hind  brain  and  cranial  nerves  of  Acipenser.    Anat.  Anz.,  Bd.  28. 

1 901.     The  brain  of  Acipenser,  etc.  Zool.  Jahrb.,  Abt.  f.  Anat.,  Bd.  15.     1902. 

Kaer,  J. 

1915.  Upper  Devonian  fish  remains  from  Ellesmere  Land.  Rep.  of  the  Second 
Norwegian  Arctic  Exped.  in  the  "Fram",  1898- 1902.  No.  33.  Publ.  by 
Videnskabs-Selskabet  i  Kristiania. 

191 6.  Spitzbergens  Devoniske  Faunaer.  i6de  Skandinaviska  Naturforskarmotet. 
Kristiania.    Forhandl. 

Kingsbury,  B.  F. 

1897.  The  structure  and  morphology  of  the  oblongata  in  fishes.  Journ.  of 
Comp.  Neurology,  Vol.  7. 

Koken,  E. 
1907.     Ueber  Hybodus,  Geol.  Palaeontol.  Abh.,  Vol.  5. 

Landacre,  F.  L. 

1916.  The  cerebral  ganglia  and  early  nerves  of  Squalus  acanthias.  Journ. 
Comp.  Neurology,  Vol.  27. 


Macropetalichthyids  and  other  Arthrodires — Stensio     195 

Lehn,  Ch. 

1918.  Beitrage  zur  Kenntnis  des  Primordialschadels  von  Polypterus.  Zeit- 
schr.  f.  angew.  Anat.  u.  Konstitutionlehre,  Vol.  2. 

Luther,  A.  F. 

1909.  Untersuchungen  uber  die  vom  N.  trigeminus  innervierte  muskulatur  der 
Selachier  (Haie  and  Rochn)  unter  Beriicksichtigung  ihrer  Beziehungen  zu 
benachbarten  Organen.     Soc.  Sci.  Fennicae,  Acta.,  Tome  36. 

Moodie,  R.  L. 

1908.     The  lateral  line  system  in  extinct  Amphibia.    Journ.  Morph.,  Vol.  14. 
1915     A    further   contribution    to   a   knowledge   of    the    lateral   line   system   in 
extinct  Amphibia.    Jour,  of  Comp.  Neurology,  Vol.  25. 

Newberry,  J.  S. 

1889.  The  Palaeozoic  fishes  of  North  America.  U.  S.  Geol.  Surv.,  Monogr., 
No.  16. 

Norris,  H.  W.,  and  Hughe,  Sally  P. 

1920.  The  cranial,  occipital,  and  anterior  spinal  nerves  of  the  Dogfish,  Squalus 
acanthias.     Journ.  of  Comp.  Neurology,  Vol.  31. 

O'Donoghue,  Ch.  H. 

1914.  Notes  on  the  circulatory  system  of  Elasmobranchs.  I.  The  venous  sys- 
tem of  the  dogfish  (Scyllium  canicula).  London.     Zool.  Soc,  Proc. 

Parker,  W.  K. 

1882.  On  the  structure  and  development  of  the  skull  in  Sturgeons  (Acipenscr 
ruthcnus  and  A.  sturio).    London.    Roy.  Soc,  Phil.  Trans.,  Vol.  173,  Part  I. 

Parker,  T.  J. 

1887.  On  the  blood-vessels  of  Mustclus  antarcticus,  etc.  London.  Roy.  Soc. 
Phil.,  Trans.,  Vol.  177.    Part  II   (1886). 

Plate,  L. 

1924.     Allgemeine  Zoologie  u.  Abstammungslehre.     Part  II.       Jena. 

Pollard,  H.  B. 

1892a.     On  the  anatomy  and  phylogenetic  position  of  Polypterus.    Zool.  Jahrb., 

Abt.  f.,  Anat.,  Bd.  5. 
1892b.     The  lateral  line  system  in  Siluroids.    Zool.  Jahrb.,  Abt.  f.  Anat.,  Bd.  5. 

Reis,  O.  M. 

1896.  Ueber  Acanthodes  bronni  Agassiz.  Morphol.  Arbeiten  herausg.  von 
Schwalbe.     Bd.  6.,  Jena. 

Retzius,  M.  G. 

1881.     Das  Gehororgan  der  Wirbelthiere,  Vol.  I.     Stockholm. 

Rex,  H. 

1891.  Beitrage  zur  Morphologie  der  Hirnvenen  der  Elasmobranchier.  Morph. 
Jahrbuch,  Bd.  17. 

Ruge,  G.  H. 

1897.  Ueber  das  peripherische  Gebiet  des  Nervus  Facialis  bei  Wirbelthieren. 
In  Festschrift  zum  siebenzigsten  Geburtstage  von  C.  Gegenbaur,  Bd.  3. 

Stensio,  E. 

1921.  Triassic  fishes   from  Spitzbergen.     Part  I.     Vienna. 

1922.  Uber  zwei  Coelacanthiden  aus  den  Oberdevon  von  Wildungen.  Palaeon- 
tologische  Zeitschrift,  Bd.  4. 

1923.  Notes  on  certain  Crossopterygians.     London.     Zool.  Soc,  Proc.  1922. 


196    Field  Museum  of  Natural  History — Geology,  Vol.  IV. 

1925.  Triassic  fishes  from  Spifzbergen.  Part  II.  Stockholm.  K.  Vet.  Akad; 
Handl.,  Ser.  Ill,  Vol.  2. 

Strong,  O.  S. 

1895.     The  cranial  nerves  of  Amphibia.     Journ.  Morph.,  Vol.  10. 

Teller,  Fr.  J. 

1891.  Ueber  den  Schadel  eines  fossilen  Dipnoers,  Ceratodus  sturii,  n.sp.  aus 
den  Schichten  der  obern  Trias  der  Nordalpen.  Wien.  Geol.  Reichsanstal, 
Abhandlungen,  Bd.  15. 

Traquair,  R.  H. 

1878.  On  the  genera  Dipterus,  Palcedaphus,  Holodus  and  Cheirodus.  Ann. 
and  Mag.  Nat.  Hist.,  Ser.  5,  Vol.  2. 

1889.  On  Homosteus  compared  with  Coccosteus,  Ag.  Geol.  Mag.,  n.s.,  del.  Ill, 
Vol.  6. 

1890.  On  the  structure  of  Coccosteus  decipiens.  Ann.  and  Mag.  Nat.  Hist., 
Ser.  6,  Vol.  5. 

Veit,  O. 

1907.     Ueber  einige   Besonderheiten  am   Primordial   Cranium  von  Lepidosteus 

osscus.    Anat.  Hefte,  Abt.  I.,  Bd.  33. 
191 1.     Beitrage  zur   Kenntnis  des  Kopfes  der  Wirbelthiere.   I.   Die  Entwick- 

lung  des  Primordial  Cranium  von  Lepidosteus  osseus.    Anat.  Hefte,  Abt.  I., 

Bd.  44- 

Vetter,  B. 

1874.     Untersuchungen  ur  vergleichenden  Anatomie  der  Kiemen-  und  Kierer- 
musculatur  der  Fische.     Teil  I.  Jen.  Zeitschr.,  Bd.  8. 

Watson,  D.  M.  S. 

1 92 1.     On  the  Coelacanth  Fish.     Ann.  and  Mag.   Nat.   Hist.,   Ser.  9,  Vol.  8. 

Watson,  D.  M.  S.  and  Day,  H. 

1 916.  Notes  on  some  Palaeozoic  fishes.  Manchester.  Lit.  &  Phil.  Soc,  Mem. 
&  Proa,  Vol.  60,  Part  I. 

Watson,  D.  M.  S.  and  Gill,  E.  L. 

1923.  The  structure  of  certain  Palaeozoic  Dipnoi.  London.  Linn.  Soc,  Journ. 
(Zool.),  Vol.  35- 

Weidenreich,  F. 

1923.  Knochenstudien  I.  t)ber  Aufbau  u.  Entwicklung  des  Knochens  u.  den 
Charakter  des  Knochengewebes.  Zeitschrift  fur  Anatomie  und  Entwick- 
lungsgeschichte,  Bd.  69. 

WlMAN,    C. 

1914.     Uber  die  Stegocephalen  aus  der  Trias  Spitzbergens.  Upsala.    Geol.  Inst., 

Bull.,  Bd.  13:1. 
1916.     Neue    Stegocephalen funde   aus    dem    Posidonomyaschiefer    Spitzbergens. 

Upsala.     Geol.  Inst.,  Bull.,  Bd.  13:2. 

White,  Ph.  J. 

1899.  The  skull  and  visceral  skeleton  of  the  Greenland  shark,  Lcemargus  mi- 
crocephalus.    Edinburgh.    Roy.  Soc,  Trans.,  Vol.  37. 

Withe,  J.  W.  van. 

1882.  Ueber  das  Visceralskelett  und  die  Nerven  des  Kopfes  der  Ganoiden  und 
von  Ceratodus.   Niederl.  Archiv.  f.  Zool.,  Bd.  5. 


Macropetalichthyids  and  other  Arthrodires — Stensio     197 

Woodward,  A.  S. 

1891.     Catalogue  of   the    fossil   fishes   in   the   British   Museum    (Natural    His- 
tory). Part  II.  London. 
1916-1919.     The  fossil  fishes  of  the  English  Wealden  and  Purbeck  formations. 
London.     Palaeont.  Soc. 

1921.  Observations  on  some  extinct  Elasmobranch  fishes.  London.  Linnean 
Soc.  Proc.     Session  133.     Presidential  address      1921 

1922.  Observations  on  Crossopterygian  and  Arthrodiran  fishes.  London.  Lin- 
nean Soc.  Proc.     Session  132     Presidential  address.     1922. 

1924.  Une  nouvel  Elasmobranche  (Bratoselache  jesuvosti  gen.  et  spec,  nov.) 
du  calcaire  carbonifere  inferiem  de  Denee.  Livre  Jubilaire  publ.  a  l'oc- 
casion  du  cinquantenaire  de  la  fondat  de  la  Soc.  Geol.  Belg.    Liege. 

Workman,  I.  S. 

1900.  The  ophthalmic  and  eye  muscle  nerves  of  the  cat-fish.  Journ.  of  Comp. 
Neurology,  Vol.  10. 


EXPLANATION  OF  PLATES 

All  the  photographs  here  shown  of  the  specimen  of  Macropeta- 
lichthys  rapheidolabis  in  the  possession  of  Field  Museum  of  Natural 
History  at  Chicago  were  made  by  the  photographic  department  of  that 
Museum.  The  other  specimens  figured  here  were  photographed  by 
myself  in  the  photographic  laboratory  of  the  Palaeozoological  Depart- 
ment of  the  Royal  State  Museum  at  Stockholm. 

In  those  cases  in  which  no  special  statements  as  to  the  scale  of  the 
figures  are  given  the  figures  have  been  reproduced  in  natural  size  or 
have  been  slightly  diminished. 

In  Fig.  4,  PI.  XXIX  and  Fig.  2,  PI.  XXXI,  the  bone  is  brighter  than 
the  stone ;  in  all  the  other  figures  the  bone  is  black  or,  in  any  case, 
darker  than  the  stone.  Sections  through  cavities  and  canals  or  exter- 
nal openings  of  canals  are  generally  shown  in  a  very  bright,  sometimes 
even  an  almost  white  tone.  Fig.  1,  PI.  XXX  is  an  exception  to  this 
however,  the  sensory  canals  and  their  tubuh  and  the  external  opening 
of  the  canal  for  the  ductus  endolymphaticus  being  black. 


EXPLANATION  OF  PLATE  XIX 

Macropctalichthys  rapheidolabis.  The  specimen  in  Field  Museum  of  Nat- 
ural History  at  Chicago  (Museum  No.  P  1154)  in,  dorsal  view.  The  dermal 
bones  of  the  cranial  roof  being  weathered  away  with  the  exception  of  the  sensory 
canal  ridges,  the  outlines  of  the  primordial  neurocranium  are  rather  clearly  ex- 
hibited. The  specimen  lacks  the  posterior  narrow  division  of  the  occipital  region, 
and  the  most  anterior  part  of  the  ethmoidal  region  is  imperfectly  preserved.  The 
ridge  for  the  hindmost  part  of  the  cephalic  division  of  the  lateral  line  has  become 
so  abraded  that  the  canals  for  nerve  branches  to  it  from  the  canal  for  the  n. 
linese  lateralis  are  clearly  seen. 

cl,  fine  canal  coming  from  below;  the  canal  probably  transmitted  a  vagus 
branch,  a  fine  branch  from  the  n.  linear  lateralis  and  perhaps  in  addition  some 
vessel ;  c.pp,  sensory  canal  commissure,  probably  corresponding  to  the  posterior 
head  line  of  pit  organs  in  fishes  in  general;  ifc,  infraorbital  sensory  canal;  Ic, 
cephalic  division  of  the  lateral  line;  Idi-ldz,  dorsally  ascending  canals  for  nerve 
branches  to  the  lateral  line;  the  canals  issue  from  the  canal  (n./)  for  the  n. 
lineae  lateralis ;  orb,  orbital  entrance ;  par,  pineal  foramen ;  soc,  supraorbital  sen- 
sory canal. 


FIELD  MUSEUM  OF  NATURAL  HISTORY. 


GEOLOGY,  VOL.   IV,   PL.  XIX. 


"I** 


c.jop 


ld\ 


LI6KAKY 

UNIVERSIIY  Of  ILLINOIS 

URBANA 


EXPLANATION  OF  PLATE  XX 

Macropetalichthys  rapheidolabis.  Same  specimen  as  in  the  preceding  plate 
but  with  a  postero-lateral  part  of  the  cranial  roof  removed  to  show  in  dorsal 
view  the  labyrinth  cavity,  a  part  of  the  cranial  cavity  and  certain  canals.  As 
all  these  structures  are  lined  by  a  thin,  perichondral  bone  layer,  which  is  black 
from  infiltration  by  bitumen,  they  consequently  appear  black  in  the  figures  ex- 
cept when  there  are  sections  through  them. 

c.ef,  canal  perhaps  traversed  by  the  arteria  efferens  hyoidea  on  its  way  to 
the  radix  aorta?  (lateral  dorsal  aorta)  ;  c.hy,  canal  for  the  vena  hyoidea  (prob- 
ably, in  the  external  part,  for  the  arteria  efferens  hyoidea  too)  ;  c.pp,  sensory 
canal  commissure,  probably  corresponding  to  the  posterior  head  line  of  pit-organs 
in  fishes  in  general ;  c.sem.ant,  division  of  the  labyrinth  cavity  for  the  canalis 
semicircularis  anterior;  cv,  cavum  cerebrale  cranii  (with  its  lining  bone  mem- 
brane) ;  only  a  posterior  part  of  it  is  seen;  d.cnd,  canal  for  the  ductus  endolym- 
phaticus,  ifc,  infraorbital  sensory  canal ;  in,  two  canals  for  nerve  branches  to 
the  infraorbital  sensory  canal.  The  direction  of  the  two  canals  makes  it  fully 
obvious  that  the  nerve-branches  transmitted  by  them  must  have  come  from  a 
prootic  nerve,  probably  the  r.  oticus  lateralis  or  its  equivalent;  /«,  the  canal 
for  the  jugular  vein;  only  the  posterior  part  behind  the  sinus  si  (see  PI.  XXII), 
shown;  lab.cav,  labyrinth  cavity  (partly  exposed.  Like  the  cavum  cerebrale  it 
has  its  lining  bone  membrane  preserved  and  is  therefore  black  in  the  figure)  : 
Ic,  cephalic  division  of  the  lateral  line;  Idi-lds,  canals  ascending  from  the  canal 
n.l.  for  the  n.  linese  lateralis  to  the  cephalic  division  of  the  lateral  line;  Is,  lamella 
of  bone  connecting  canals  transmitting  lateralis  branches  for  the  innervation  of  the 
posterior  part  of  the  internal  and  external  bone  layers  with  each  other ;  orb,  orbital 
entrance ;  par,  pineal  foramen ;  soc,  supraorbital  sensory  canal ;  v.lb,  canal  from 
the  labyrinth ;  cavity  to  the  dorsal  part  of  the  proximal  portion  of  the  vagus  canal. 
The  canal  probably  transmitted  a  vein.  On  the  right  side  the  canal  is  partly  seen 
in  section  close  to  its  posterior  end;  X™,  the  canal  for  the  vagus  and  the  vena 
cerebralis  posterior  (proximal  part). 


FIELD  MUSEUM  OF  NATURAL  HISTORY. 


GEOLOGY,  VOL.   IV,   PL.   XX. 


par 


C.se/n.aat 


■ 


-SOC 


,lfc 


m 


** 


-c.pp 


Id 


r\^  \      !      Xv/l 

\idj  i  is 


i** 


LIBKAKY 

UNIVERSUY  Of  ILLINOIS 

URBANA 


EXPLANATION  OF  PLATE  XXI 

Macropctalichthys  raphcidolabis.  Same  specimen  as  in  Pis.  XIX  and  XX. 
Primordial  neurocranium  in  ventral  view.  Certain  parts  of  the  left  side  (right 
in  the  figure)  and  of  the  anterior  end  removed. 

c.car.ext,  canal  for  the  arteria  carotis  external  (represented  merely  by  a 
groove,  as  its  filling  of  stone  and  its  external  wall  have  been  destroyed  by 
weathering)  ;  c.car.int,  canal  for  the  arteria  carotis  interna  (represented  to  a 
large  extent  by  its  filling  of  stone,  as  its  external  wall  has  been  abraded).  The 
most  anterior  white  spot  marks  the  place  at  which  the  internal  carotid  curved 
upward  to  the  cavum  cerebrale;  c.com,  canal  for  the  arteria  carotis  communis 
(its  external  wall  and  in  part  also  its  stone  filling  destroyed.  In  the  anterior 
part,  in  which  the  stone  filling  is  lost,  it  appears  as  a  groove)  ;  c.hy,  canal  for 
the  vena  hyoidea  (merely  the  proximal  part  completely  preserved  in  the  figure, 
the  distal  part  being,  as  is  well  seen,  represented  there  by  a  groove)  ;  c.ophth.lat, 
canal  for  the  n.  ophthalmicus  lateralis  (anterior  part)  ;  c.paU  the  canal  for  the 
r.  palatinus  facialis  through  the  orbital  floor  (dorsal  opening)  ;  era,  canal  for 
the  radix  aortae  (lateral  dorsal  aorta).  The  canal  is  imperfectly  preserved, 
being  represented  merely  by  a  groove  in  the  figure ;  csem,  division  of  the  labyrinth 
cavity  for  a  semicircular  canal,  probably  the  c.  semicircularis  externas ;  cv,  cavum 
cerebrale  cranii  (merely  a  small  posterior  part  is  shown)  ;  dtx,  indication  of  a 
canal,  perhaps  for  the  lateralis  branch  that  accompanied  the  n.  glossopharyngeus 
from  the  cavum  cerebrale;  jgx,  canal  for  the  jugular  vein  from  the  orbit  to  the 
mandibular  vein  (section)  ;  ju,  canal,  which  through  its  anterior  opening  trans- 
mitted the  vena  mandibularis  (the  anterior  part  not  fully  preserved.  The 
anterior  opening  was  situated  more  laterally  than  in  the  figure)  ;  jih  and  jih,  an- 
terior and  posterior  opening  of  the  canal  ju;  na,  nasal  aperture;  nf,  nasal  fon- 
tanelle ;  n.L,  canal  for  the  n.  linae  lateralis ;  olf,  olfactory  capsule ;  rm,  ophth.  lat, 
branch  for  a  lateralis  nerve  from  the  canal  for  the  n.  ophthalmicus  lateralis  to  the 
supraorbital  sensory  canal ;  si,  sinus  formed  by  the  confluence  of  the  canal  ju  and 
the  canal  era  (its  ventral  wall  has  been  removed,  so  that  its  stone  filling  covered 
by  the  lining  membrane  of  bone  is  visible)  :  soc,  supraorbital  sensory  canal  (a 
small  anterior  part)  :  s.ra,  groove  for  the  radix  aortae  (lateral  dorsal  aortae)  ;  Sx, 
groove  anterior  of  the  external  opening  of  the  vagus  canal ;  VII,  canal  for  the 
n.  facialis  on  the  left  side — right  in  the  figure — the  external  part  in  section; 
IX,  canal  for  the  n.  glossopharyngeus  (external  opening)  ;  X™,  external  opening 
of  the  canal  for  the  vagus  and  the  vena  cerebralis  posterior. 


FIELD  MUSEUM  OF  NATURAL  HISTORY 

olf 


GEOLOGY,   VOL.    IV,    PL.  XXI. 


c.ophth.lat 

rm.ophth.la.t 


-c.car.int 


LIBRARY 
cRSiTY  Of  ILLINOIS 
URBANA 


EXPLANATION  OF  PLATE  XXII 

Macropetalichthys  rapheidolabis.  Same  specimen  as  in  the  three  preceding 
plates.  Imperfect  impression  of  the  ventral  surface  of  the  primordial  neuro- 
cranium  with  certain  lateral  parts  of  this  remaining  in  their  original  position  on 
the  left  side. 

c.car.int,  canal  for  the  arteria  carotis  interna  (the  white  opening  denoted 
is  the  place  at  which  the  artery  turned  upwards  and  ascended  to  the  cavum 
cerebrale)  ;  c.hy,  canal  for  the  venal  hyoidea  (on  the  right  side  is  the  external 
opening  shown  as  impression)  ;  c.cf,  canal  perhaps  for  the  arteria  efferens  hyoidea 
on  its  way  to  the  radix  aortae  (lateral  dorsal  aorta)  ;  c.ophthJat,  canal  for  the 
n.  ophthalmicus  lateralis;  c.ophth.sup.Vf,  canal  perhaps  for  the  r.  ophthalmicus 
superficialis  V  through  the  antorbital  process  (merely  the  anterior  opening  seen 
as  impression  in  the  figure)  ;  c.pah,  canal  for  the  r.  palatinus  facialis  through 
the  orbital  floor  (merely  the  ventral  opening  into  the  internal  carotid  canal  is 
seen  here)  ;  era,  canal  for  the  radix  aortae  (lateral  dorsal  aorta)  ;  ifc,  infraor- 
bital sensory  canal ;  in,  two  canals  for  nerve  branches  to  the  infraorbital  sen- 
sory canal.  The  direction  of  the  canals  makes  it  fully  evident  that  the  nerve 
branches  transmitted  by  them  must  have  come  from  a  prootic  nerve,  probably 
the  r.  oticus  lateralis  or  its  equivalent;  jg,  canal  for  the  vena  jugular  is  from  the 
orbit  to  the  mandibular  vein  (section)  :  ju,  canal  for  the  jugular  vein  pos- 
terior of  the  sinus  si;  juu  anterior  opening  of  the  canal  ju.  The  opening  was 
traversed  by  the  mandibular  vein  (impression)  ;  olf,  olfactory  capsule  (impres- 
sion of  ventral  side)  ;  si,  sinus  arisen  by  the  confluence  of  the  canals  ju  and 
era;  s.pal,  groove  for  the  r.  palatinus  facialis  on  the  lower  side  of  the  primor- 
dial' neurocranium  (seen  as  impression  here  and  therefore  appearing  as  a  ridge)  ; 
s.ra,  groove  for  the  radix  aortae  (lateral  dorsal  aorta).  The  groove  is  preserved 
as  an  impression  and  has  therefore  the  shape  of  a  ridge;  VII,  canal  for  the 
n.  facialis  (section)  ;  IX,  canal  for  the  n.  glossopharyngeus  (section  close  at  the 
external  opening  into  the  groove  s.ra;  Xvn,  canal  for  the  vagus  and  the  vena 
cerebralis  posterior    (abraded  impression  of   the  left  external  opening). 


FIELD  MUSEUM  OF  NATURAL  HISTORY. 


GEOLOGY.  VOL.   IV,   PL.  XXII. 


ophth.lat 


jyr^j***sp 


ophth 


s  r<x 


LIBRARY 

UNIVERSITY  OF  ILLINOIS 

URBANA 


191 


EXPLANATION  OF  PLATE  XXIII 

Macropetalichthys  rapheidolabis.  Same  specimen  as  in  the  preceding  plates. 
The  primordial  neurocranium  in  ventral  view  with  certain  parts  removed  on 
the  left  side  (right  in  the  figure)  to  show  the  cavum  cerebrale  and  the  exits 
of  the  canals  for  the  cranial  nerves  from  this. 

afr,  acustico-facialis  recess;  a.opt,  division  of  the  external  opening  of  the 
opticus  canal  traversed  by  the  arteria  optica;  c.car.ext,  canal  for  the  arteria 
carotis  externa  (as  its  filling  of  stone  and  ventral  wall  have  been  destroyed,  it 
appears  as  a  groove  in  the  figure)  ;  c.car.int,  canal  for  the  arteria  carotis  in- 
terna. On  the  right  side  (left  in  the  figure)  the  suborbital  part  is  in  almost  the 
entire  extension  represented  by  the  filling  of  stone,  as  the  ventral  wall  has  been 
destroyed.  The  foramen  somewhat  in  front  of  the  stone  filling  is  the  place 
at  which  the  artery  curved  upward  to  ascend  to  the  cavum  cerebrale.  On  the 
left  side  (the  right  in  the  figure)  is  seen  the  ascending  part  of  the  same  canal; 
c.com,  canal  for  the  arteria  carotis  communis  (in  its  anterior  part,  in  which  the 
ventral  wall  and  stone  filling  have  been  destroyed,  it  appears  as  a  groove,  in  its 
posterior  part,  in  which  merely  the  external  wall  is  lacking,  the  filling  of  stone 
is  clearly  seen)  ;  c.hy,  canal  for  the  vena  hyoidea  (the  distal  part  destroyed  and 
represented  in  the  figure  merely  as  a  groove)  ;  c.ophth.lat,  canal  for  the  n.  oph- 
thalmicus lateralis  (merely  an  anterior  part  and  a  posterior  part  discernible)  ; 
c.ophth.prof,  canal  for  the  r.  ophthalmicus  profundus  (proximal  part)  ;  c.ophth. 
sup.V,  canal  for  the  r.  ophthalmicus  superficialis  trigemini  to  the  orbit  (entire 
canal  with  the  external  opening)  ;  c.ophth.  sup.  Vf,  canal  probably  for  the 
r.  ophthalmicus  superficialis  trigemini  through  the  preorbital  process ;  era,  canal 
for  the  radix  aortae  (lateral  dorsal  aorta).  Its  external  wall  and  filling  being 
destroyed  it  appears  merely  as  a  groove;  cv,  cavum  cerebrale  cranii  (with  its 
lining  membrane  of  bone — the  inner  bone  layer)  ;  dn,  indication  of  a  canal  to 
the  dorsal  side  of  the  cranial  roof,  probably  for  a  lateralis  branch  that  accom- 
panied the  n.  glossopharyngeus  from  the  cavum  cerebrale;  jih,  anterior  opening 
of  the  canal  ju  (as  the  lateral  parts  are  broken  off  the  actual  anterior  opening 
of  the  canal  ju  was  situated  more  laterally  than  in  the  figure.  We  are  there 
in  fact  concerned  with  a  section  through  the  part  of  the  canal  ju  situated  an- 
terior of  the  sinus  si)  ;  jih,  position  of  the  posterior  opening  of  the  canal  ju 
(the  external  wall  and  the  filling  of  stone  being  destroyed,  only  a  groove  is 
seen  at  this  place  in  the  figure)  ;  na,  nasal  aperture;  nf,  nasal  fontanelle;  n.l, 
canal  for  the  n.  lineae  lateralis ;  olf,  olfactory  capsule ;  rm.ophth.lat,  fine  canal  for 
a  branch  from  the  n.  ophthalmicus  lateralis  to  the  supraorbital  sensory  canal; 
si,  sinus  in  the  lateral  wall  arisen  by  confluence  of  the  canals  ju  and  era;  soc, 
supraorbital  sensory  canal  (anterior  part)  ;  s.ra,  groove  for  the  radix  aortae 
(lateral  dorsal  aorta)  ;  S*,  groove  leading  from  the  vagus  canal ;  I,  canal  for 
the  tractus  olfactorius;  II,  canal  for  the  n.  opticus  (entire  canal  with  external 
opening)  ;  III,  canal  for  the  n.  oculimotorius ;  V,  trigeminus  recess ;  Vi,  i  canal  for 
the  r.  maxillaris  and  r.  mandibularis  trigemini  (section  through  the  proximal 
part)  ;  VII,  canal  for  the  n.  facialis  (proximal  part  in  section)  ;  VIII,  canal  for 
the  n.  acusticus ;  IX,  canal  for  the  glossopharyngeus  (proximal  part)  ;  Xtd,  canal 
for  the  n.  vagus  and  the  vena  cerebralis  posterior. 


FIELD  MUSEUM  OF  NATURAL  HISTORY. 


GEOLOGY,   VOL.    IV,   PL.    XXIII. 
cophth.'ar 

;  rmophT'i  I  at 
,-Soc 


7,1 


LIBRARY 
UNIVERSITY  OF  ILLINOIS 

URBANA 


EXPLANATION  OF  PLATE  XXIV 
Macropetalichthys  rapheidolabis.     Same  specimen  as  in  the  preceding  plates. 
Fig.  I.     Primordial  neurocranium  seen  from  the  right  side. 

Fig.  2.  A  transversal  section  through  the  lateral  part  of  the  primordial  neu- 
rocranium, along  the  canal  for  the  n.  vagus  and  the  vena  cerebralis  posterior.  The 
impression  of  the  anterior  side  of  this  canal  is  shown  in  black.  In  one  place  a 
part  of  its  filling  of  stone  remains   (with  white  external  end). 

Fig.  3.  Primordial  neurocranium  in  posterior  aspect.  The  place  from  which 
the  posterior  narrow  division  of  the  occipital  region  issues  is  well  shown.  Further, 
we  can  see  at  this  place  the  posterior  end  of  the  middle  division  of  the  cavum 
cerebrale  and  a  section  through  the  cavum  cerebrale  at  the  transition  to  the 
posterior  narrow  division  (white).  The  canal  for  the  n.  lineae  lateralis  is  ex- 
posed during  a  rather  large  part  of  its  course,  as  the  cranial  wall  has  been 
destroyed  at  this  place. 

c.hy,  canal  for  the  vena  hyoidea  (the  septum  between  it  and  the  anterior 
opening  of  the  canal  ju,  partly  destroyed)  ;  c. 0 phth.su p. V,  canal  through  the 
preorbital  process,  probably  for  the  r.  ophthalmicus  superficialis  trigemini;  c.pp, 
sensory  canal  commissure,  probably  corresponding  to  the  posterior  head  line  of 
pit  organs  in  fishes  in  general;  cv,  cavum  cerebrale  cranii  (a  section  of  it  at 
the  transition  to  the  posterior  narrow  division  is  shown  in  white)  ;  dix. indication 
of  a  canal  to  the  dorsal  side  of  the  primordial  neurocranium.  The  canal  pro- 
bably transmitted  a  lateralis  branch  that  might  have  accompanied  the  n.  glosso- 
pharyngeus  from  the  cavum  cerebrale;  dx,  dorsal  branch  from  the  vagus  canal 
for  a  lateralis  nerve;  dxn,  and  dn>,  branches  of  the  canal  ds,  the  former  of 
which  lodged  the  nerve  to  the  antero-laterally  running  part  of  the  cephalic  di- 
vision of  the  lateral  line,  while  the  latter  lodged  the  nerve  to  the  sensory  canal 
commissure  c.pp;  ifc,  infraorbital  sensory  canal ;  jui,  anterior  opening  of  the 
canal  ju  (the  septum  between  it  and  the  external  part  of  the  canal  c.hy,  partly 
destroyed);  Ic,  cephalic  division  of  the  lateral  line;  ldi-lde,  canals  for  branches 
from  the  n.  lineas  lateralis  to  the  most  posterior  part  of  the  cephalic  division  of 
the  lateral  line ;  na,  nasal  aperture ;  nf,  nasal  f ontanelle ;  n.l,  canal  for  the  lineae 
lateralis  (exposed  in  the  distal  part  owing  to  the  incomplete  state  of  preservation  of 
the  posterior  cranial  wall ;  orb,  orbit ;  v. lb,  canal  from  the  postero-dorso-medial 
part  of  the  labyrinth  cavity  to  the  proximal  dorsal  part  of  the  vagus  canal.  The 
canal  probably  transmitted  a  vein  (section)  ;  vy,  opening  of  a  canal  of  doubtful 
importance  (perhaps  for  some  vessel)  ;  VII,  canal  for  the  n.  facialis;  XV,  canal 
for  the  n.  glossopharyngeus ;  Xvn,  canal  for  the  n.  vagus  and  the  vena  cerebralis 
posterior   (the  two  divisions  are  clearly  shown). 


LIBRARY 

UNIVERSITY  OF  ILLINOIS 

URBANA 


EXPLANATION  OF  PLATE  XXV 
Macropetalichthys  rapheidolabis.   Same  specimen  as  in  the  preceding  plates. 

Fig.  i.  Primordial  neurocranium  from  the  left  side  with  certain  lateral  parts 
removed  to  show  parts  of  the  cavum  cerebrale. 

Fig.  2.  Primordial  neurocranium  in  the  same  aspect  as  in  the  preceding  figure 
but  with  still  another  lateral  part  removed  to  show  the  interorbital  wall. 

Fig.  3.  The  surface  orp  in  fig  1,  seen  from  behind.  This  surface  is  the 
impression  of  the  posterior  surface  of  the  orbit. 

afr,  acustico-facialis  recess ;  a.opt,  division  of  the  external  opening  of  the 
opticus  canal  for  the  arteria  optica ;  c.car.int,  canal  for  the  arteria  carotis  in- 
terna (the  ascending  portion)  ;  c.ophth.lat,  canal  for  the  n.  ophthalmicus  lateral- 
is (proximal  part)  ;  c.ophth.prof,  canal  for  the  r.  ophthalmicus  profundus  to  the 
orbit  (proximal  part)  ;  c.ophth.sup.V,  canal  for  the  r.  ophthalmicus  superficialis 
trigemini  to  the  orbit;  cv,  cavum  cerebrale  (middle  division,  which  is  covered 
by  its  lining  layer  of  bone — the  inner  bone  layer)  ;  jg,  canal  for  the  jugular  vein 
from  the  orbit  to  the  confluence  with  the  mandibular  vein ;  na,  nasal  aperture ; 
orb,  orbit.  In  fig.  1  it  is  filled  with  stone,  in  fig.  2  this  filling  has  been  re- 
moved so  that  its  medial  wall  is  seen  partly  with  its  external  surface  preserved 
(black,  as  it  is  covered  by  the  external  bone  layer)  and  partly  in  section  (bright, 
with  nerve  canals  in  it)  ;  orp,  posterior  surface  of  the  orbit  preserved  as  an  im- 
pression (to  a  large  extent  with  the  external  bone  layer  adherent  to  it  and  there- 
fore black  in  the  figure)  ;  v.lb,  canal  from  the  postero-dorso-medial  part  of  the 
labyrinth  cavity  to  the  proximal  dorsal  part  of  the  vagus  canal.  The  canal 
probably  transmitted  a  vein  (here  is  merely  seen  a  section  through  the  posterior 
part)  ;  Vt,  Vi,  two  canals  leading  from  the  cavum  cerebrale  to  the  labyrinth  cavity, 
probably  for  vessels ;  II,  canal  for  the  n.  opticus  (external  opening)  ;  III,  canal 
for  the  n.  oculomotorius ;  V,  trigeminus  recess ;  Vs,  $,  canal  for  the  r.  maxillaris 
trigemini  and  the  r.  mandibularis  trigemini  (section  through  the  proximal  part)  ; 
VII,  facialis  canal  (several  parts  of  it  are  seen).  Figs.  I  and  2  show  that  it  is 
crossed  on  the  dorsal  side  by  the  canal  jg;  VIII,  canal  for  the  n.  acusticus;  IX, 
canal  for  the  n.  glossopharyngeus  (proximal  part)  ;  Xvn,  canal  for  the  n.  vagus 
and  the  v.  cerebralis  posterior. 


LIBRARY 

UNIVERSITY  OF  ILLINOIS 

URBANA 


EXPLANATION  OF  PLATE  XXVI 
Macropetalichthys  rapheidolabis.     Same  specimen  as  in  the  preceding  plates. 
Figs.  1, 2.    The  cavum  cerebrale  seen  from  the  left  side   (partly  in  section). 

Fig.  3.  The  labyrinth  cavity  seen  from  the  medial  side  with  the  wall  separat- 
ing it  from  the  orbit  (the  posterior  surface  of  the  orbit  denoted  by  orp)  and 
the  vagus  canal   (Xvn,)   shown  in  their  positions  and  with  their  real  thickness. 

Fig.  4.  The  labyrinth  cavity  shown  from  the  lateral  side  (imperfectly  ex- 
posed). 

afr,  acustico-f acialis  recess ;  c.ophth.prof,  canal  for  the  r.  ophthalmicus  pro- 
fundus to  the  orbit  (proximal  part)  ;  c.ophth.sup.V,  canal  for  the  r.  ophthalmi- 
cus superficialis  trigemini  to  the  orbit  proximal  part)  ;  csem,  divisions  of  the 
labyrinth  cavity  for  a  semicircular  canal,  perhaps  the  c.  semicircularis  externas ; 
csem.  ant,  division  of  the  labyrinth  cavity  for  the  canalis  semicircularis  anterior ; 
cv,  cavum  cerebrale  (with  its  lining  bone  layer — the  inner  bone  layer — where  it  is 
shown  in  black ;  sections  through  it  are  shown  in  white)  ;  d.end,  canal  for  the 
ductus  endolymphaticus ;  ep,  diverticle  from  the  posterior  part  of  the  roof  of 
the  anterior  division  of  the  cavum  cerebrale  (not  seen  in  its  entire  length  in  the 
figures)  ;  orp,  posterior  surface  of  the  orbit;  par,  pineal  canal;  ru,  division  of 
the  labyrinth  cavity  occupied  by  the  recessus  utriculi;  utr,  division  of  the  laby- 
rinth cavity  occupied  by  the  utriculus ;  sac,  division  of  the  labyrinth  recess 
occupied  by  the  sacculus  (partly  seen)  ;  v. lb,  canal  from  the  labyrinth  cavity  to 
the  dorsal  proximal  part  of  the  vagus  canal  (probably  for  a  vein)  ;  v*,  Vxx,  canals 
probably  for  vessels ;  Vi,  Vz,  canals  probably  for  vessels  from  the  cavum  cerebrale 
to  the  labyrinth  cavity ;  I,  canal  for  the  tractus  olfactorius ;  III,  canal  for  the 
n.  oculomotorius  (proximal  part)  ;  V,  trigeminus  recess ;  V»,  »,  canal  for  the  r. 
maxillaris  trigemini  and  the  r.  mandibulars  trigemini  (proximal  part  in  section)  ; 
VII,  canal  for  the  n.  facialis  (in  fig.  3  a  considerable  part  of  it  is  seen  in  the  wall 
between  the  labyrinth  cavity  and  the  orbit,  as  the  ventral  part  of  this  wall  has 
been  removed)  ;  VIII,  canal  for  the  n.  acusticus ;  IX,  canal  for  the  n.  glosso- 
pharyngeus;  X™,  canal  for  the  n.  vagus  and  the  vena  cerebralis  posterior  (in 
figs.  1,  2,  section  through  its  proximal  part,  in  figs.  3,  4,  impression  of  its  anterior 
side.  In  fig.  4  also,  a  part  of  its  stone  filling  is  seen,  the  anterior  end  of  which 
is  white). 


LIBRARY 

UNIVERSITY  OF  ILLINOIS 

URBANA 


EXPLANATION  OF  PLATE  XXVII 

Macropetalichthys  rapheidolabis.  Specimen  710  F  in  the  American  Museum 
of  Nat.  Hist.,  New  York.    About  34  of  the  nat.  size. 

The  specimen  exhibits  certain  basal  parts  of  the  primordial  neurocranium. 

cv,  cavum  cerebrale  cranii,  the  posterior  narrow  division  (in  section  at  the 
place  denoted.  Behind  this  place  covered  by  the  internal  bone  layer  il)  ;  el,  the 
external  bone  layer  (the  part  of  it  on  the  ventral  surface  of  the  occipital 
labyrinth  and  orbitotemporal  regions  and  a  part  of  it  on  the  dorsal  side  of  the 
occipital  region  preserved.  The  latter  part  has,  however,  been  partly  removed 
by  preparation)  ;  il,  internal  bone  layer  (surrounding  the  posterior  narrow  divi- 
sion of  the  cavum  cerebrale)  ;  lab.cav,  labyrinth  cavity  (in  horizontal  section)  ; 
Idi,  canal  for  a  nerve  branch  from  the  n.  linese  lateralis  to  the  posterior  part  of 
the  cephalic  division  of  the  lateral  line;  n.l,  canal  for  the  n.  linese  lateralis  (its 
origin  from  the  vagus  canal  clearly  seen  here)  ;  orb,  orbit  (its  floor  partly  pre- 
served on  the  left  side)  ;  I,  canal  for  the  tractus  olf actorius ;  IX  ?,  perhaps  the 
canal  for  the  n.  glossopharyngeus ;  X-m,  canal  for  the  n.  vagus  and  the  vena  cere- 
bralis  posterior. 


FIELD   MUSEUM   OF  NATURAL  HISTORY. 


GEOLOGY,  VOL.    IV,   PL.  XXVII. 


LIBRARY 

UNIVERSITY  OF  ILLINOIS 

URBANA 


EXPLANATION  OF  PLATE  XXVIII 

Figs.  I,  2.  Epipetalichthys  ivildungensis.  Specimen  belonging  to  the  Geologi- 
cal Institution  of  the  University  of  Greifswald,  Germany.  Fig.  i  shows  the 
parts  preserved  of  the  ethmoidal  region  of  the  primordial  neurocranium  from  the 
right  side;  fig.  2  shows  the  parts  preserved  of  the  occipital  and  labyrinth  regions 
in  ventral  aspect. 

Figs.  3,  4.  Macropetalichthys  rapheidolabis.  Specimen  4445  G  of  the  Ameri- 
can Museum  of  Nat.  Hist.,  New  York.  Fig.  3  is  in  posterior,  fig.  4  in  ventral 
view.  The  specimen  displays  the  posterior  narrow  division  of  the  occipital  region 
of  a  rather  large  animal. 

Fig.  5.  Macropetalichthys  rapheidolabis.  Specimen  280  G  of  the  American 
Museum  of  Nat.  Hist.  New  York.  Portion  of  the  posterior  narrow  division  of 
the  occipital  region  in  ventral  view.  The  ventral  parts  of  the  division  and  the 
cavum  cerebrale  have  been  removed  so  that  merely  certain  dorsal  parts  remain. 
What  is  lettered  el  is  here  the  anterior  part  of  the  external  bone  layer  of  the 
dorsal  side  of  the  division.  The  bone  piece  lettered  it  is  a  posterior  part  of  the 
inner  bone  layer  on  the  dorsal  side  of  the  cavum  cerebrale. 

ch,  space  for  the  notochord  (just  at  the  anterior  end)  ;  ch.w,  ridge  in  the 
anterior  part  of  the  haemal  groove  caused  by  the  notochord;  c.rai,  c.rai,  anterior 
and  posterior  opening  of  a  canal  for  the  radix  aortae  (lateral  dorsal  aorta).  The 
canal  corresponds  to  a  posterior  part  of  the  groove  s.ra  in  M.  rapheidolabis ;  cr.ol, 
crista  occipitalis  lateralis ;  cr.sp,  craniospinal  process  (impression  of  its  anterior 
surface;  fragments  in  fig.  3);  el,  external  bone  layer;  hcem,  haemal  groove;  il, 
internal  bone  layer;  na,  nasal  aperture;  orb,  orbital  entrance;  pr,  postero-laterally 
projecting  process  of  the  anterior  broad  division  of  the  occipital  region. 


LIBRARY 

UNIVERSITY  OF  ILLINOIS 

UR8ANA 


. 


EXPLANATION   OF   PLATE   XXIX 

Figs,  i,  2.  Macropetalichthys  agassisif  Specimen  in  the  possession  of  Mr. 
S.  Junkermann  of  Bielefeld,  Germany.  Fig.  i  shows  much  crushed  posterior 
parts  of  the  primordial  neurocranium  in  ventral  view ;  fig.  2  a  posterior  part  of 
the  dermal  cranial  roof  with  a  number  of  sensory  canal  pores. 

Figs.  3,  4.  Epipetalichthys  wildungensis.  Specimen  belonging  to  the  Geo- 
logical Institution  of  the  University  of  Greifswald,  Germany.  Same  specimen 
as  in  figs.  I,  2,  PI.  XXVIII.  Fig.  3  shows  the  part  preserved  of  the  ethmoidal 
region  in  ventral  view,  fig.  4  the  ornament  on  a  part  of  the  dermal  cranial  roof 
(impression  with  the  bone  tissue  of  the  tubercles  adhering  to  the  stone  and 
appearing  brighter  than  this). 

c.pp,  sensory  canal  commissure  probably  corresponding  to  the  posterior  head 
line  of  pit  organs  in  fishes  in  general;  cr.od,  crista  occipitalis  dorsalis  (impres- 
sion) ;  d.end,  dorsal  opening  of  the  canal  for  the  ductus  endolymphaticus ;  Ic, 
cephalic  division  of  the  lateral  line;  na,  nasal  aperture;  olf,  olfactory  capsule; 
pr,  postero-laterally  projecting  process  of  the  broad  anterior  division  of  the 
occipital  region;  s.pal,  groove  for  the  r.  palatinus  facialis. 


LIBRARY 

UNIVERSITY  Of  ILLINOIS 

URBANA 


EXPLANATION  OF  PLATE  XXX 

Fig.  i.  Epipetalichthys  wildungensis.  Specimen  belonging  to  the  Geological 
Institution  of  the  University  of  Greifswald,  Germany.  Same  specimen  as  in 
figs,  i,  2,  PI.  XXVIII  and  figs.  3,  4  in  PI.  XXIX.  Head  in  dorsal  view.  The 
head  lacks  a  large  posterior  part.  Anteriorly  it  shows  the  cavum  precerebrale 
and  the  olfactory  capsule.  The  approximate  position  of  the  sutures  between  the 
bones  of  the  dermal  cranial  roof  is  indicated  with  black  lines. 

Fig.  2.  Macropetalichthys  rapheidolabis.  Specimen  280  G  of  the  American 
Museum  of  Nat.  Hist.,  New  York.  The  posterior  end  of  the  occipital  region  in 
posterior  views.  The  cranio-spinal  process  {cr.sp)  is  well  shown,  but  is  repre- 
sented only  by  the  impression  of  its  anterior  side. 

Mi,  Mt,  Li,  L2,  L»,  Pi,  P2,  S,  dermal  bones  of  the  cranial  roof ;  Mi  imper- 
iect  anteriorly;  cr.od,  crista  occipitalis  dorsalis  (its  posterior  continuation  on 
the  anterior  surface  of  the  cranio-spinal  process)  ;  cr.sp,  cranio-spinal  process 
(represented  merely  by  the  impression  of  its  anterior  surface)  ;  d.end,  the  canal 
for  the  ductus  endolymphaticus  (dorsal  opening)  ;  ifc,  infraorbital  sensory  canal 
(its  position  indicated  by  its  pores)  ;  il,  internal  bone  layer;  Ic,  cephalic  division 
of  the  lateral  line  (its  posterior  part  indicated  by  pores;  its  anterior  part  does 
not  open  outwards);  olf,  olfactory  capsule;  orb,  orbital  entrance;  pfg,  cavum 
precerebrale;  soc,  supraorbital  sensory  canal  (exposed  to  a  large  extent  by 
weathering)  st.com,  cross-commissural  sensory  canal,  probably  representing  the 
true  supratemporal  commissure  of   fishes  in  general. 


FIELD  MUSEUM  OF  NATURAL  HISTORY. 


GEOLOGY,  VOL.    IV,   PL.  XXX. 


pSs 


d.en  <£■      Zc 


crod 


en 


T-sjo 


ifc 


LIBRARY 

UNIVERSITY  Of  ILLINOIS 

URBANA 


9dl 


EXPLANATION  OF  PLATE  XXXI 

Fig.  I.  Macropetalichthys  rapheidolabis.  Microscopic  section  through  the 
external  bone  layer  of  the  primordial  neurocranium.     Magnification  700/1. 

Fig.  2.  Epipetalichthys  wildungensis.  Specimen  belonging  to  the  Geological 
Institution  of  the  University  of  Greifswald,  Germany.  Part  of  a  section  through 
the  anterior  part  of  the  posterior  narrow  division  of  the  occipital  region.  Note 
the  trabecles  on  the  inside  of  the  external  bone  layer  {el)  and  on  the  outside  of 
the  notochordal  layer  (ch.l).     Magnification  about  30/1. 

ch,  space  for  the  notochord  (partly  seen);  ch.l,  bone  layer  surrounding  the 
notochordal  space;  cs,  cell  space;  el,  external  bone  layer;  ham,  haemal  groove. 


FIELD  MUSEUM  OF  NATURAL  HISTORY. 


GEOLOGY,  VOL.   IV,  PL.  XXXI. 


-Vi 


CS- 


-*a 


